Allow format selection in get_opts

Default is "value".

Change-Id: I244253f6cd53104a57ef12f6b14e1653c89d38bc

Author: kromanenko

functional/common/test.py

@@ -58,8 +58,9 @@ def get_openstack_configuration_value(cls, configuration):
         return cls.openstack('configuration show ' + opts)
 
     @classmethod
-    def get_opts(cls, fields):
-        return ' -f value ' + ' '.join(['-c ' + it for it in fields])
+    def get_opts(cls, fields, format='value'):
+        return ' -f {0} {1}'.format(format,
+                                    ' '.join(['-c ' + it for it in fields]))
 
     @classmethod
     def assertOutput(cls, expected, actual):