Revert "Revert "uncap pbr and sqla requirements""
Revert "Revert "uncap pbr and sqla requirements""

This reverts commit e4d0e5be8d0d154eaec1ae0bb156d1c7485043b9

Now that flake8-related dependencies have been updated in the
dependent change the pep8 job is fixed.

Change-Id: Idfa6a18836d7ce02dfaa5d9da1a51c98ad987f51

rcherrueau/sqlalchemy-migrate,andras-tim/sqlalchemy-migrate,stackforge/sqlalchemy-migrate,openstack/sqlalchemy-migrate,openstack/sqlalchemy-migrate,rcherrueau/sqlalchemy-migrate