Missing description of Performa tool in the Tools section

[Dina Belova]

Right now we're having http://docs.openstack.org/developer/performance-docs/methodologies/tools.html# section will performance and scale testing tools descriptions. In the Message queue HA test plan http://docs.openstack.org/developer/performance-docs/test_plans/mq_ha/plan.html *performa* tool is mentioned http://docs.openstack.org/developer/performance-docs/test_plans/mq_ha/plan.html#tools - it looks like its description will better fit to the specialized section.