[Openstack libs] hot fix for python2.7 venv

To avoid failures for python 2.7 venv due
`TypeError: 'encoding' is an invalid keyword argument for this function`
reason: usptream warlock package release:

https://github.com/bcwaldon/warlock/commit/4241a7a9fbccfce7eb3298c2abdf00ca2dede64a

Prod-related: PROD-30416 (PROD:30416)

Change-Id: I17ca18665596a76610773080738aa0cd794033b4
1 file changed