Do not install pip in heat config element

Since this element depends on os-apply-config and os-refresh-config, and
the two depends on pip-and-virtualenv. pip command has been installed in
pip-and-virtualenv.

If we install pip via install-packages here, for these images which have
no python-pip in repository, the installation will fail.

Change-Id: I4284bdd293213321751439272bad439e2a899005
Closes-Bug: #1352689
Merge "Do not install pip in heat config element"