Remove unneeded device_owner field from l2pop tuple

The DVR development added this device_owner to the middle of this
tuple during early development because it was thought to be needed.
Over the course of development, it was found to be unnecessary and
much of the code that read it from this value was removed or
obsoleted.  That job went unfinished and so this commit completes it.
This essentially restores the code to what it was before and fixes the
regression that was caused.

Change-Id: Ia901f925883b53e9880dd25688e16e0ffe402bf4
Partial-bug: #1352801
Return port context from _bind_port_if_needed

Previously port was returned causing exception being thrown
in rpc handling code.

Change-Id: Iba498d0600d625f0469392b99ac0bc8c1f1ecff7
Closes-Bug: #1354912
NSX: fix wording for configuration option

This patch clarifies that in order to use NSX distributed
routers, the replication_mode parameter should be set to
'service'. This is already its default value, so no further
change is needed beyond clarifying wording.

Change-Id: I446c428ecf8c0bf7f6947e69562d60a7fb4383ed
Closes-Bug: #1355502
Make plugin and l3plugin available as mixin's properties

This makes the code simpler and slightly more efficient.
This is a minor refactoring related to a race condition
observed when the agent is processing a router while its
interfaces are being removed.

Related-bug: #1355409

Change-Id: Ic0ce25aa6a977e28b1ab76081c74da4c46c2ca6b
Raise exception for network delete with subnets presents

N1kv plugin should raise an exception during network delete
if there is a subnet that is tied to that network.

Changed the order of the Assert arguments since now it's encoraged to have <expected_value, actual_value> now.

Change-Id: I92f177af0e2a2fbc460e0d668989ce590b7d1cb2
Closes-Bug: 1336107
Merge "Return port context from _bind_port_if_needed"
Merge "Make plugin and l3plugin available as mixin's properties"
Merge "Raise exception for network delete with subnets presents"
Merge "NSX: fix wording for configuration option"
Merge "Remove unneeded device_owner field from l2pop tuple"