Bump minimum pbr version to 0.6 and requ argparse module

Matches Global Requirements.In the elastic-recheck project pbr version does
not match the global requirements. No require argparse module.

Change-Id: I5f565c882317a992b645be3b578f2d6a78487690
Merge "Bump minimum pbr version to 0.6 and requ argparse module"