Update desired virtualenv version everywhere

1.10.1 can't handle the oslo pre-release situation, since it has
pip 1.4 which doesn't grok wheels. We only have 1.10.1 on Centos
nodes right now - all the rest of them have 1.11.4 and are working
properly.

Change-Id: I406719e819f80f1bd5203d283d305e13fd2b7351
Merge "Update desired virtualenv version everywhere"