Add unit tests for doctor's caching symptoms
Add unit tests for doctor's caching symptoms

Currently there are no unit tests for any of doctors symptoms. This
patch is only adding unit tests for the caching symptoms and more
will be released for each symptom group in doctor.

Change-Id: I177ef91206bcad095be06b0607c04c1547994146
Partial-Bug: #1641621

mahak/keystone,ilay09/keystone,mahak/keystone,openstack/keystone,mahak/keystone,openstack/keystone,rajalokan/keystone,rajalokan/keystone,rajalokan/keystone,ilay09/keystone,openstack/keystone,ilay09/keystone