When pip installed version does not support the
--upgrade-strategy (system installed version vs
venv installed one) we need to fallback into
case previous to 4d0c892e1054453774122a5aeefe0d3c26a35e91
Without this fix, Bifrost installation with Keystone
enabled and venv activated fails in task
bifrost-keystone-install : Install from /opt/stack/keystone using pip
with --upgrade-strategy unkown option
Change-Id: Ib5da14ba5048e48c66070c6d2a7f51aa6688a7d9
483e3a7a6f