azure devops extension to support --service-principal login

**Describe the bug**
az login --service-principal --username xxx --password yyy --tenant zzz
--> Login goes successful.

az devops configure --defaults organization=https://xyz project=xyz
--> This works fine.

az pipelines build list -o table --verbose --debug
--> Error:
```
Current cloud config:
AzureCloud
trying to get token (temp) for tenant 05d75c05-fa1a-42e7-9cf1-eb416c396f2d and user fc7bc748-404e-4f72-84e2-95cb6f2edb2f
attempting to read file /root/.azure/accessTokens.json as utf-8-sig
adal-python : 2e75d6f5-b4a6-46da-b9ca-0a2b5cea63eb - Authority:Performing instance discovery: ...
adal-python : 2e75d6f5-b4a6-46da-b9ca-0a2b5cea63eb - Authority:Performing static instance discovery
adal-python : 2e75d6f5-b4a6-46da-b9ca-0a2b5cea63eb - Authority:Authority validated via static instance discovery
adal-python : 2e75d6f5-b4a6-46da-b9ca-0a2b5cea63eb - TokenRequest:Getting token from cache with refresh if necessary.
adal-python : 2e75d6f5-b4a6-46da-b9ca-0a2b5cea63eb - CacheDriver:finding with query keys: {'_clientId': '...', 'userId': '...'}
adal-python : 2e75d6f5-b4a6-46da-b9ca-0a2b5cea63eb - CacheDriver:Looking for potential cache entries: {'_clientId': '...', 'userId': '...'}
adal-python : 2e75d6f5-b4a6-46da-b9ca-0a2b5cea63eb - CacheDriver:Found 0 potential entries.
not able to get token from az login
Could not retrieve token from local cache. Please run 'az login'.
Traceback (most recent call last):
File "/root/.azure/cliextensions/azure-devops/azext_devops/dev/common/services.py", line 157, in get_token_from_az_login
auth_token = profile.get_access_token_for_resource(user, tenant, '499b84ac-1321-427f-aa17-267ca6975798')
File "/usr/lib/python2.7/site-packages/azure/cli/core/_profile.py", line 506, in get_access_token_for_resource
username, tenant, resource)
File "/usr/lib/python2.7/site-packages/azure/cli/core/_profile.py", line 916, in retrieve_token_for_user
" Please run 'az login'." if not in_cloud_console() else ''))
CLIError: Could not retrieve token from local cache. Please run 'az login'.
```
As per ERROR, when service principal is used for `az login`, then token is not retrieved. However it works fine if normal user is used. I have these steps in automation pipeline, where there is no human interaction.

**To Reproduce**
Azure Cli Version: 2.0.76

Azure-Devops extension version:
Use az --version
Look for something like-
Extensions:
azure-devops (0.14.0)

Steps to reproduce the behavior:
1. az login
2. az devops configure defaults.
3. Try any `az pipelines` command
4. See error

**Expected behavior**
It should return data