extension initdevbox deployment failed in concourse-ci template

[concourse-ci](https://github.com/Azure/azure-quickstart-templates/blob/master/concourse-ci/azuredeploy.json)

### Issue Details
When I try to deploy concourse-ci template to azure, initdevbox extension failed with following message:

> {"code":"DeploymentFailed","message":"At least one resource deployment operation failed. Please list deployment operations for details. Please see https://aka.ms/arm-debug for usage details.","details":[{"code":"Conflict","message":"{\r\n \"status\": \"Failed\",\r\n \"error\": {\r\n \"code\": \"ResourceDeploymentFailure\",\r\n \"message\": \"The resource operation completed with terminal provisioning state 'Failed'.\",\r\n \"details\": [\r\n {\r\n \"code\": \"VMExtensionProvisioningError\",\r\n \"message\": \"VM has reported a failure when processing extension 'initdevbox'. Error message: \\\"Enable failed: failed to execute command: command terminated with exit status=1\\n[stdout]\\nacking azure-mgmt-logic==0.30.0rc1 (from azure-mgmt==0.30.0rc1->azure==2.0.0rc1)\\nDownloading/unpacking azure-mgmt-network==0.30.0rc1 (from azure-mgmt==0.30.0rc1->azure==2.0.0rc1)\\nDownloading/unpacking azure-mgmt-notificationhubs==0.30.0rc1 (from azure-mgmt==0.30.0rc1->azure==2.0.0rc1)\\nDownloading/unpacking azure-mgmt-redis==0.30.0rc1 (from azure-mgmt==0.30.0rc1->azure==2.0.0rc1)\\n Downloading azure_mgmt_redis-0.30.0rc1-py2.py3-none-any.whl\\nDownloading/unpacking azure-mgmt-resource==0.30.0rc1 (from azure-mgmt==0.30.0rc1->azure==2.0.0rc1)\\nDownloading/unpacking azure-mgmt-scheduler==0.30.0rc1 (from azure-mgmt==0.30.0rc1->azure==2.0.0rc1)\\nDownloading/unpacking azure-mgmt-storage==0.30.0rc1 (from azure-mgmt==0.30.0rc1->azure==2.0.0rc1)\\n Downloading azure_mgmt_storage-0.30.0rc1-py2.py3-none-any.whl\\nDownloading/unpacking azure-mgmt-web==0.30.0rc1 (from azure-mgmt==0.30.0rc1->azure==2.0.0rc1)\\nRequirement already satisfied (use --upgrade to upgrade): msrestazure>=0.1.0 in /usr/local/lib/python2.7/dist-packages (from azure-graphrbac==0.30.0rc1->azure==2.0.0rc1)\\nDownloading/unpacking azure-common>=1.1.0 (from azure-graphrbac==0.30.0rc1->azure==2.0.0rc1)\\n Downloading azure_common-1.1.12-py2.py3-none-any.whl\\nRequirement already satisfied (use --upgrade to upgrade): requests in /usr/local/lib/python2.7/dist-packages (from azure-servicebus==0.20.1->azure==2.0.0rc1)\\nDownloading/unpacking azure-nspkg (from azure-storage==0.30.0->azure==2.0.0rc1)\\n Downloading azure_nspkg-2.0.0-py2.py3-none-any.whl\\nDownloading/unpacking futures (from azure-storage==0.30.0->azure==2.0.0rc1)\\n Downloading futures-3.2.0-py2-none-any.whl\\nDownloading/unpacking python-dateutil (from azure-storage==0.30.0->azure==2.0.0rc1)\\nDownloading/unpacking azure-mgmt-nspkg (from azure-mgmt-authorization==0.30.0rc1->azure-mgmt==0.30.0rc1->azure==2.0.0rc1)\\n Downloading azure_mgmt_nspkg-2.0.0-py2.py3-none-any.whl\\nRequirement already satisfied (use --upgrade to upgrade): six>=1.5 in /usr/lib/python2.7/dist-packages (from python-dateutil->azure-storage==0.30.0->azure==2.0.0rc1)\\nInstalling collected packages: azure, azure-mgmt, azure-graphrbac, azure-servicebus, azure-storage, azure-servicemanagement-legacy, azure-mgmt-authorization, azure-mgmt-cdn, azure-mgmt-compute, azure-mgmt-logic, azure-mgmt-network, azure-mgmt-notificationhubs, azure-mgmt-redis, azure-mgmt-resource, azure-mgmt-scheduler, azure-mgmt-storage, azure-mgmt-web, azure-common, azure-nspkg, futures, python-dateutil, azure-mgmt-nspkg\\n Running setup.py install for azure\\n Could not find .egg-info directory in install record for azure==2.0.0rc1\\n Running setup.py install for azure-mgmt\\n Could not find .egg-info directory in install record for azure-mgmt==0.30.0rc1 (from azure==2.0.0rc1)\\nSuccessfully installed azure azure-mgmt azure-graphrbac azure-servicebus azure-storage azure-servicemanagement-legacy azure-mgmt-authorization azure-mgmt-cdn azure-mgmt-compute azure-mgmt-logic azure-mgmt-network azure-mgmt-notificationhubs azure-mgmt-redis azure-mgmt-resource azure-mgmt-scheduler azure-mgmt-storage azure-mgmt-web azure-common azure-nspkg futures python-dateutil azure-mgmt-nspkg\\nCleaning up...\\nSuccessful\\nOperation: pip install netaddr==0.7.18, Retry #0\\nDownloading/unpacking netaddr==0.7.18\\nInstalling collected packages: netaddr\\nSuccessfully installed netaddr\\nCleaning up...\\nSuccessful\\nStart to generate SSH key pair for BOSH...\\nGenerating public/private rsa key pair.\\nYour identification has been saved in bosh.\\nYour public key has been saved in bosh.pub.\\nThe key fingerprint is:\\n77:d3:ca:3f:49:bb:2e:32:09:46:5f:68:0f:fd:56:a8 \\nThe key's randomart image is:\\n+--[ RSA 2048]----+\\n| |\\n| |\\n| o . |\\n| . + o.. .|\\n| .So.+oo.. |\\n| o..oEo+ |\\n| . . .oo o |\\n| + ..+ |\\n| o o+o |\\n+-----------------+\\nStart to run setup_env.py...\\nPrepare Bosh deployment script and manifest\\nPrepare Concourse deployment script and manifests\\nInstall bosh-init\\nStart to update Ruby 1.9 to 2.0 ...\\n*** CURRENT SOURCES ***\\n\\nhttps://rubygems.org/\\nUpdating rubygems-update\\n\\n[stderr]\\ndpkg-preconfigure: unable to re-open stdin: No such file or directory\\n/usr/local/lib/python2.7/dist-packages/requests/packages/urllib3/util/ssl_.py:318: SNIMissingWarning: An HTTPS request has been made, but the SNI (Subject Name Indication) extension to TLS is not available on this platform. This may cause the server to present an incorrect TLS certificate, which can cause validation failures. You can upgrade to a newer version of Python to solve this. For more information, see https://urllib3.readthedocs.io/en/latest/security.html#snimissingwarning.\\n SNIMissingWarning\\n/usr/local/lib/python2.7/dist-packages/requests/packages/urllib3/util/ssl_.py:122: InsecurePlatformWarning: A true SSLContext object is not available. This prevents urllib3 from configuring SSL appropriately and may cause certain SSL connections to fail. You can upgrade to a newer version of Python to solve this. For more information, see https://urllib3.readthedocs.io/en/latest/security.html#insecureplatformwarning.\\n InsecurePlatformWarning\\n/usr/local/lib/python2.7/dist-packages/requests/packages/urllib3/util/ssl_.py:122: InsecurePlatformWarning: A true SSLContext object is not available. This prevents urllib3 from configuring SSL appropriately and may cause certain SSL connections to fail. You can upgrade to a newer version of Python to solve this. For more information, see https://urllib3.readthedocs.io/en/latest/security.html#insecureplatformwarning.\\n InsecurePlatformWarning\\nunable to write 'random state'\\nunable to write 'random state'\\nunable to write 'random state'\\nunable to write 'random state'\\nunable to write 'random state'\\nunable to write 'random state'\\nunable to write 'random state'\\nunable to write 'random state'\\nERROR: While executing gem ... (NameError)\\n uninitialized constant Gem::SafeYAML\\n\\\".\"\r\n }\r\n ]\r\n }\r\n}"}]}

Start with concourse-ci/azuredeploy.json and inspect the initdevbox extension command, then trace setup_env.py through the reported deployment output. Focus on the Ruby 1.9-to-2.0 update and the Gem::SafeYAML failure; done means the template deployment completes without the initdevbox provisioning error.

Written by the indexing model from the issue text.