Update Testing.md to factor out Strainer
Update Testing.md to factor out Strainer

* remove refs to Strainer
* add steps for testing
* remove knife test as it's not used in gates anymore

Change-Id: I12cbeddd5a0c9809c971838f308410b4242a5f0c
Partial-Bug: #1350470

mattray/cookbook-openstack-ops-messaging