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.

Thanks for your comment. 
I have added the workaround because i saw (and quoted) token expiry error triggering despite this line:
https://github.com/bitbar/testdroid-api-client-python/blob/master/testdroid/__init__.py#L130
In other words: what you say should happen, isn't happening. I urge you to comment out the workaround and see for yourself. You need a relatively long-running job. 

Note that I have now added an additional commit (added the result download function)