Replace basestring with six.string_types
Replace basestring with six.string_types

six.string_types
  Possible types for text data. This is basestring() in Python 2
  and str in Python 3.

Partial implements: blueprint py33-support

Change-Id: I25b463efdfe2e20af92dd805d4f44b40d4bd4b35

Tesora/tesora-python-troveclient,metacloud/python-troveclient,Tesora/tesora-python-troveclient,openstack/python-troveclient,openstack/python-troveclient,metacloud/python-troveclient