Jenkins with SSH deployment fails at VMExtensionsFailure

101-jenkins-with-ssh-public-key (https://raw.githubusercontent.com/Azure/azure-quickstart-templates/master/101-jenkins-with-ssh-public-key/azuredeploy.json)

### Issue Details

{"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 'jenkinsInit'. Error message: \\\"Enable failed: failed to execute command: command terminated with exit status=100\\\".\"\r\n }\r\n ]\r\n }\r\n}"}]}

Start with 101-jenkins-with-ssh-public-key/azuredeploy.json and inspect the jenkinsInit VM extension referenced by the deployment. Reproduce the deployment, use the ARM deployment operations guidance in the issue to identify the command returning exit status 100, and consider the issue done when SSH deployment completes without VMExtensionsFailure.

Written by the indexing model from the issue text.