Stop using master for pip
Stop using master for pip

Rally cannot work via latest pip:
  [r.name.lower() for r in pip.req.parse_requirements(
  rally AttributeError: 'module' object has no attribute 'req'

Badly it forbids building containers from a gerrit change.

Change-Id: Ie60344b2a7793729823643ba2c1d3c30500d56c4
Signed-off-by: Cédric Ollivier <d48310251a4a484d041bc5d09a9ac4d86d20f793@orange.com>

opnfv/functest,mywulin/functest,mywulin/functest,opnfv/functest