The most recent version of pip (1.2.1 as of a couple days ago) fails
to install the required Cinder .venv packages. Nailing the installed
pip version when using run_tests.sh seems like a reasonable solution
to this issue.
Fixes LP Bug #1047120.
Change-Id: I8d831f747b0d25b5d0f6e74a234e764ff448965b