Bug 1254 - Added unit tests for FlowConvertor, NotificationQueueWrapper and OpenflowPluginProvider

 - also fixed OFToMDSalFlowConvertorTest - instruction type in testToSALInstruction()
   was not set correctly

Change-Id: I3fb7a1a4d3c94d3c01ebf707d0d0d9431f56a17b
Signed-off-by: Michal Polkorab <michal.polkorab@pantheon.sk>