Fix typo and add test for refresh_instance_security_rules

Change Ia36b0dfb adds virt driver API method
refresh_instance_security_rules but there is a typo in the method's
docstring and it needs to be covered in test_virt_drivers.py.

Closes-Bug: #1290036

Change-Id: Idacffe2087f0bec6290e3422d1e777376b489615
Merge "Fix typo and add test for refresh_instance_security_rules"