Bug-1421 - Chaining of results and updateFlow

1. Chained the flowmod results when more than one flows are added/updated
2. Fixed updateFlow when match/priority were changed. After RemoveFlow, add flow was being passed in as null.
3. Create a common set of methods to be used for both add and update flow tasks

Change-Id: I5d3576150bc5da79764c1b311e9c51df387f8c6f
Signed-off-by: Kamal Rameshan <kramesha@cisco.com>