install_pip: don't fail when not installed
install_pip: don't fail when not installed

On some platforms, "python -m pip" isn't available.  Currently this is
run undconditionally from the "get_versions" function; remove the call.

Change-Id: I91d6c66d055f02fa7b4368593b629933f82d8117

openstack-dev/devstack,nawawi/openstack,nawawi/openstack,openstack-dev/devstack