Add unit test for convert_protocol
Add unit test for convert_protocol

Add test cases of unit test for convert_protocol.
convert_protocol method has some conditional branches.
However, currently, unit test is missing that verification whether
those conditional branches correctly behave.

Change-Id: Idec82a8c45b8db15293ff6ac5b954f5d40f3af54

openstack/neutron-fwaas,openstack/neutron-fwaas