Restrict prettytable to >=0.6,<0.8.

Match the openstack/requirements version of prettytable in pip-requires
to avoid version conflicts.

Change-Id: I78f3c6ef9a9a8d35939eb100827e429c12a0a60d
Merge "Restrict prettytable to >=0.6,<0.8."
Add find() method to CrudManager

Add a find() methods to CrudManager to maintain compatability
with existing CLI lookups using utils.find_resource().

Change-Id: Ia9b38b975bb88fb361f3471b66f98c7e81bbc6de
attempt to add tests

Change-Id: I5915a2da7c296cb7ae773ba7682860570b8c20a8