Be explicit about the identity plugin required in unit tests

This change fixes UT failures introduced by os-client-config===1.27.0
(and [1] in particular) that was masking the fact that these tests
were not specifying the required 'token' identity plugin.

[1] e6755872ad

Change-Id: I9521a7e1bff39c1d25b998ca12c450890517fd2f

neutronclient/tests/unit/test_shell.py

@@ -233,6 +233,7 @@ class ShellTest(testtools.TestCase):
 
         options.update(base_options)
         if options.get('os_token'):
+            options.update({'auth_type': 'token'})
             options.update({'os_token': 'token', 'os_url': 'url'})
         else:
             options.update({'os_token': None, 'os_url': None})