Run pip check at end of devstack

The new pip depsolver is coming this summer. Until it's ready,
run pip check at the end of devstack to make sure we're not
somehow installing conflicting package versions. We shouldn't
be, because of constraints, but if we are, better to know and
start figuring it out.

Change-Id: Id98f0848ff5a252d93e5f8029df2d069924d603f
2 files changed