Remove negative test framework documentation
Remove negative test framework documentation

We have a conclusion to remove the description of negative test
framework during Austin summit, details at:
https://etherpad.openstack.org/p/newton-qa-negative-testing

Change-Id: Ia3d36b8d1c8e9721b88dbc35bc350af822b8dc6f

Juniper/tempest,masayukig/tempest,masayukig/tempest,vedujoshi/tempest,openstack/tempest,sebrandon1/tempest,sebrandon1/tempest,bigswitch/tempest,bigswitch/tempest,cisco-openstack/tempest,Tesora/tesora-tempest,Tesora/tesora-tempest,Juniper/tempest,cisco-openstack/tempest,vedujoshi/tempest,openstack/tempest