Refactor common parts of client tests
Refactor common parts of client tests

Refactored common parts of client tests.

Change-Id: Id63c3a9cf5d6d3cdb2298cafd1925cd4040f0115
Signed-off-by: Andras Kovi <65f87d134de1fcfde6fa6765899f8e63327f6140@nokia.com>

StackStorm/python-mistralclient,openstack/python-mistralclient,StackStorm/python-mistralclient,openstack/python-mistralclient