Do not download wheels when running "pip install"

Virtualenv has recently been upgraded to 1.11, which comes with pip 1.5. In
this version of pip, if 'pip install' can find a wheel, it downloads it instead
of the tar.gz. This is an issue since the version of pip used in the gates can
still be too old to work with wheels by default.

Use '--no-use-wheel' in the 'pip install' command to fix this.

Closes-Bug: #1276242
Change-Id: I00a32b3abd3b08703f66834ae30e6c4b0cf7bd7d