Waiting for test-run completion

It's difficult to use the python client for test-run completion. 
One needs to write a bash script that parses the stdout coming out from various commands:
- the one that schedules the job (to extract the job id)
- one that enquires the state of the job (to extract its status)
This cannot be done with python if only, because start_test_run does not return the job id (it only prints it out). 
Since anyone using this client will be interested in knowing when the job is finished, i thought I propose to enable it at the very root and propose this change.

This should not happen as self.get_token() is called before each HTTP request, and get_token uses refresh token to retrieve a new token if the current one is expired. The expiration time for refresh token in our backend is currently 3600seconds so if the access token is expired the new access token is retrieved: 
https://github.com/bitbar/testdroid-api-client-python/blob/master/testdroid/__init__.py#L130