OVS Agent: limit veth names to 15 chars

The maximum length of a veth interface name is 15 characters.
This patch limits the length of the veth names created for
integration bridges by switching to a fixed-length hashing
mechanism if the normal name would exceed the allowed length.

Closes-Bug: #1328288
Change-Id: I432cee62a6dc91f268becbc91f8024c23dd0bfac
(cherry-picked from 1222366f6dadf7ce2a810c919344054196134db8)
Big Switch: fix capabilities retrieval code

References the raw REST response in the capabilities
parsing code so json.loads doesn't get an object
that may already be decoded and fail.

Conflicts:
	neutron/tests/unit/bigswitch/test_capabilities.py
	neutron/tests/unit/bigswitch/test_servermanager.py

Closes-Bug: #1326173
Change-Id: Ia3179b7499f35a6ab2e9ce1631ab15ed27d64647
Remove RPC to plugin when dhcp sets default route

_set_default_route() was using an RPC to the plugin to get the DHCP
port for the network on the current host, and then used it to form
the tap device name. This happened on every allocation reload too.
This fix removes the RPC and gets the tap device name using local
methods instead. It also removes an unnecessary call to set the
default route in the restart method.

Closes-Bug: 1290068
Related-Bug: 1294254
Change-Id: I639bcf93725c4969d1011d2d20491d461ccfdbed
(cherry picked from commit 9dbd1e5e5a41eff88a044b8de992d2f1f14898b3)
Merge "OVS Agent: limit veth names to 15 chars" into stable/icehouse
Merge "Big Switch: fix capabilities retrieval code" into stable/icehouse
Merge "Remove RPC to plugin when dhcp sets default route" into stable/icehouse
Merge branch 'stable/icehouse' of https://github.com/openstack/quantum into stable/icehouse