Fix neutron cli tests skip for testr

The manner in which a skip exception was raised in the neutron cli
tests would cause the tests to be listed as fail when run with testr.
This commit corrects the behavior so that testr will correctly mark
the test as skipped instead of failed.

Change-Id: I9680b6946b44eeab9a0e6c5b9b4609e702880f07
1 file changed