Workaround pip issue 4059

[hannes-ucsc]

Symptom:

http://jenkins.cgcloud.info/job/toil-pull-requests/2029/testReport/src.toil.test.src.resourceTest/ResourceTest/testVirtualEnv/

Upstream ticket:

pypa/pip#4059

We should prevent the latest pip from being installed in the virtualenv.

[cket]

Does this need to be backported? It seems to be showing up on the 3.3.x branch
http://jenkins.cgcloud.info/job/toil-pull-requests/2059/testReport/junit/src.toil.test.src.resourceTest/ResourceTest/testVirtualEnv/

[hannes-ucsc]

Yes. Cherrypicking won't work, though as the changes are scattered around. For the original fix I search for all occurrences of virtualenv. Would mind taking this over?

[cket]

Sure, I'll take it