Moved out common testcases from test_type_vxlan.py

This patch-set will refactor the test_type_vxlan.py and test_type_gre.py.

We need to add testcases for TunnelRpcCallbackMixin() so better we
should move common test cases from test_type_vxlan.py to test_type_tunnel.py and
add testcases for TunnelRpcCallbackMixin() into it.

Partial-Bug: #1381071
Change-Id: I81f8930cf665ccd89c03f0bd2199ce5d1d9dff65
Subnet delete for IPv6 SLAAC should not require prior port disassoc

With the current Neutron implementation, a subnet cannot be deleted
until all associated IP addresses have been remove from ports (via
port update) or the associated ports/VMs have been deleted.

In the case of SLAAC-enabled subnets, however, it's not feasible to
require removal of SLAAC-generated addresses individually from each
associated port before deleting a subnet because of the multicast
nature of RA messages. For SLAAC-enabled subnets, the processing of
subnet delete requests needs to be changed so that these subnets will
be allowed to be deleted, and all ports get disassociated from their
corresponding SLAAC IP address, when there are ports existing on
the SLAAC subnet.

Change-Id: I281f5a1553248e09174dc49d0a42aef4b5c44bee
Closes-Bug: 1393435
ofagent: Remove obsolete bridge_mappings (agent side)

For ofagent, it has been superseded by physical_interface_mappings
and was planned to be removed in Kilo.

Related: blueprint ofagent-physical-interface-mappings
Change-Id: I68c7e9991a3dc14ccad709ed1a438c7c45420dd6
Merge "Moved out common testcases from test_type_vxlan.py"
Merge "ofagent: Remove obsolete bridge_mappings (agent side)"
Merge "Subnet delete for IPv6 SLAAC should not require prior port disassoc"