Tests: Fix ofproto/trace and expose megaflows when having a set action.

ofproto/trace incorrectly reported the megaflow based on the modified
flow, rather than the original flow key.  Now the original flow key is
stored before any modifications and is used for reporting the megaflow.

Also, flow reporting is suppressed only for resubmit flows, so that
the final flow will be printed if it is different from the incoming
flow key.

Test for the megaflow key and mask with flows having set actions.
This helps in verifying the correctness of operation with masked set
actions in the following patches.

Signed-off-by: Jarno Rajahalme <jrajahalme@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>