Add add_boolean_argument method if missing

This method is persent in python-neutronclient version
2.3.12 but not in 2.3.9. So if the later version is
present in a deployment, we add this method via this
patch.

Change-Id: I3c3cb398b7fb5eaf39504412567d78c4fcf365c3
Closes-bug: 1518671

gbpclient/common/utils.py

@@ -11,10 +11,22 @@
 #    under the License.
 #
 
-
+import argparse
+from neutronclient.common import utils as n_utils
 import re
 
 
+if not hasattr(n_utils, 'add_boolean_argument'):
+    def add_boolean_argument(parser, name, **kwargs):
+        for keyword in ('metavar', 'choices'):
+            kwargs.pop(keyword, None)
+        default = kwargs.pop('default', argparse.SUPPRESS)
+        parser.add_argument(name, metavar='{True,False}',
+                            choices=['True', 'true', 'False', 'false'],
+                            default=default, **kwargs)
+    n_utils.add_boolean_argument = add_boolean_argument
+
+
 def str2dict(strdict):
     """Convert key1=value1,key2=value2,... string into dictionary.