Fix errors reported by pyflakes.
Fix errors reported by pyflakes.

* openstack/common/setup.py
  get_reqs_from_files(): Remove unused variable.
  get_reqs_from_files(): Use local variables in a conventional
  way, to prevent errors like:
  local variable 'datestamp' is assigned to but never used.

Change-Id: I44e137d383b96e1601b7bded1e36e84ff14a8f68

openstack-dev/pbr,WiFast/pbr,klmitch/pbr,varunarya10/pbr,JioCloud/pbr,redhat-openstack/pbr,emonty/oslo-packaging,WiFast/pbr,redhat-openstack/pbr,openstack-dev/pbr,emonty/oslo-packaging,citrix-openstack-build/pbr,varunarya10/pbr,JioCloud/pbr,klmitch/pbr,citrix-openstack-build/pbr,citrix-openstack-build/pbr,openstack-dev/pbr