Avoid error in rbtools.clients.tfs if "tf" returns 1
Review Request #9995 — Created June 2, 2018 and submitted — Latest diff uploaded
If "tf" returns 1, the TFS client may error out with: ``` ERROR: Could not load SCM Client "tfs" Traceback (most recent call last): File "[...]/rbtools/clients/__init__.py", line 397, in load_scmclients client = ep.load()(config=config, options=options) File "[...]/rbtools/clients/tfs.py", line 972, in __init__ if 'Version Control Tool, Version 15' in tf_vc_output: TypeError: argument of type 'NoneType' is not iterable ``` because of `none_on_ignored_error=True` immediately above.
Ran unit tests