Stale VXLAN and GRE tunnel port/flow deletion

Stale VXLAN and GRE tunnel port/flow deletion

Description:
Stale GRE and VXLAN tunnel endpoints persists in neutron db this should be
deleted from the database. Also, if local_ip of L2 agent changes the
stale tunnel ports and flows persists on br-tun on other Compute Nodes and
Network Nodes for that remote ip this should also be removed.

Implementation

Plugin changes:
The plugin side changes are covered in following patch-set
https://review.openstack.org/#/c/121000/.

Agent changes:
Added tunnel_delete rpc for removing stale ports and flows from br-tun.
tunnel_sync rpc signature upgrade to obtain 'host'.
Added testcases for TunnelRpcCallbackMixin().

This patch-set agent deals with agent side changes.

Closes-Bug: #1179223
Closes-Bug: #1381071
Closes-Bug: #1276629

Co-Authored-By: Aman Kumar <amank@hp.com>
Co-Authored-By: phanipawan <ppawan@hp.com>
Change-Id: I291992ffde5c3ab7152f0d7462deca2e4ac1ba3f