Sync requirements with global requirements

Sync requirements.txt and test-requirements from global
OpenStack requirements repository.

The oslo.db >= 0.4.0 is needed by the recent patch to fix
the testsuite (https://review.openstack.org/116192).

Change-Id: I429dee9caf8c32963da683d596e25b14f62f77ee
Merge "Sync requirements with global requirements"