Add negative UT cases for subnet/GW create/update

When force_gateway_on_subnet is configured, ensure
that a GW with IP same as subnet, and BCAST GW IP
are rejected during subnet create. For subnet update,
ensure GW outside of subnet is rejected.

bug 1178675

Change-Id: Ice58f7e1be7966b247c165e52807405401e5a4ea
Fix logic in test_db_loadbalancer

Fix code to check HTTP error code before attempt to deserialize body

fixes bug 1180113

Change-Id: I1d75e0fe739dfa70ef415602e669319797af026f
relax amqplib and kombu version requirements

as nova did while ago.

this particular version of kombu doesn't work if newer msgpack happens
to be installed on the system.

bug 1178512

Change-Id: I2749623036723b5a772b1c4c01dc07437e421925
Fix linuxbridge RPC message format

The linuxbridge, openvswitch, and hyperv plugins all use the same
basic RPC interface between their plugins and L2 agents. But the
attributes describing a virtual network passed from the plugin to the
agent over this interface differed for historical reasons. The
openvswitch and hyperv plugins each pass network_type,
physical_network, and segmentation_id attributes, whereas the
linuxbridge plugin previously passed vlan_id and physical_network
attributes, using special vlan_id values to indicate flat or local
network types.

This patch changes the linuxbridge plugin to pass network_type and
segmentation_id attributes instead of the vlan_id attribute, bringing
its message formats into sync with the other plugins. RPC
compatibility is required for blueprint modular-l2 so that the ml2
plugin can work with all three existing types of L2 agent. This RPC
message format change is also required for blueprint
vxlan-linuxbridge.

Unlike the vxlan-linuxbridge patch on which it is based (see
https://review.openstack.org/#/c/26516/), this patch does not bump the
linuxbridge RPC version number, as the ml2 plugin will require all
three L2 agents to use the same RPC version. Instead, the updated
linuxbridge agent maintains compatibility with old linuxbridge plugins
by accepting either the old or new attributes. There is also a
configuration option, currently turned on by default, to enable the
updated linuxbridge plugin to pass the vlan_id attribute expected by
old linuxbridge agents along with the new attributes. These message
format compatibility mechanisms are intended to aid during upgrades,
and can eventually be removed.

Change-Id: I7cc1c9f96b09db6bab2c7d9f2b30b79fa4dab919
Merge "Fix linuxbridge RPC message format"
Merge "Fix logic in test_db_loadbalancer"
Merge "relax amqplib and kombu version requirements"
Merge "Add negative UT cases for subnet/GW create/update"