BUG 2862 - alien flow ID when priority is missing.

BUG 2862 - alien flow ID when priority is missing.

Problem was:
- flow was sent to device
- attempt to write flow registry - fails (NPE) because missing priority
- flow was written to device
- statistics bring info about flow
- flow isn't found in flow registry therefore alien ID is generated for it.

Solution:
- sending of flow to device is executed only after storing flow to flow
registry. If it is unsuccessful then nothing is sent to device. Flow is thus
stored only in config DS.

Change-Id: I371d4030c41ac0866fb3615b8c2380aef5b283e2
Signed-off-by: Jozef Gloncak <jgloncak@cisco.com>