Compare requirements case insensitively.

Pip treats package names as case insensitive which has resulted in
different cases being used in the various project requirements files.
Use a case insensitive comparison when comparing a project against
openstack/requirements to avoid invalid comparison failures.

Change-Id: I59b3362ffb68d1c4662ac5d94919de47f0506218
Reviewed-on: https://review.openstack.org/25639
Reviewed-by: Khai Do <zaro0508@gmail.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Approved: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins