Remove discover from test-requirements
Remove discover from test-requirements

It's only needed for python < 2.7 which is not supported

Change-Id: Idfc1677ca01853993e21f4c8aa50a9be66c32203

Tesora/tesora-python-troveclient,openstack/python-troveclient,openstack/python-troveclient,Tesora/tesora-python-troveclient