Work around OS X 10.11 bug with check_install()

Review Request #8058 — Created March 15, 2016 and submitted — Latest diff uploaded

Information

RBTools
master
28be9b8...

Reviewers

This has been fixed upstream (http://bugs.python.org/issue26083) but who
knows when Apple will update their version of Python they distribute so
this change simply works around the issue by treating a ValueError to be
the same as an OSError. This fix seems smaller/safer then switching to 
the subprocess32 package as it adds another external dependency an the 
documentation states that it hasn't been tested on Windows.
Before my fix, when running rbt post, I get:
  ValueError: insecure string pickle
(I don't have tfs installed)

After my fix, running rbt post works fine.