Use python2 for dib images
Use python2 for dib images

zuul-cloner is currently only compatible with python2 so ensure the
pip/virtualenv that dib sets up is in python2

Signed-off-by: Jamie Lennox <1b9801e8e46f6bd96338b24e58c84c4f37762fc2@gmail.com>

BonnyCI/hoist,jamielennox/hoist,SpamapS/hoist,SpamapS/hoist,BonnyCI/hoist,jamielennox/hoist