Add a Tunnel end-point variable for Neutron configuration

The HOST_IP address is being used as IP address
for end-point tunnel configruation. A new variable is
needed to specify a different IP address for the tunnel
end-point that Neutron will use

Change-Id: Ic7fb4853df167e78bf882af6a712b903db754dc2
Closes-bug: #1340433
Fix Neutron configuration if Ceilometer is enabled

Previously if Ceilometer service was enabled,
configuration option to enable Neutron network
notifications was not set. This fixes it.

Change-Id: Ia53d9db1828ef2daa0ce637b2a2635795856502c
Closes-Bug: #1340754
FAQ: Clarification - Devstack is a gating project

Change-Id: I52fdfc5c865e864939df49fecb71b8e615a28cbf
Support multiple Cinder backend types

This is the first step in supporting multiple Cinder backend types at
once.  It initially converts the existing hard-coded multi-lvm support
to a new cinder_backends driver form.  Eventually the cinder_plugins
will be converted to this form so they can be enabled more than just
one at a time using CINDER_ENABLED_BACKENDS.

The default configuration should be identical to the previous defaults,
including for both True and False values of CINDER_MULTI_LVM_BACKEND.

The existing cinder_plugins are expected to be removed when this is
complete. They should continue to work until they have been converted.

Add wait for c-api to ensure it is started before continuing.

Change-Id: I93b8ef32832269d730c76a6dc24ddb4f20c6d9df
Merge "Add a Tunnel end-point variable for Neutron configuration"
Merge "Support multiple Cinder backend types"
Merge "Fix Neutron configuration if Ceilometer is enabled"
Merge "FAQ: Clarification - Devstack is a gating project"
Add $NOVA_VNC_ENABLED to force VNC on.

This allows multinode setups to function correctly without enabling n-novnc on
pure compute nodes.

Change-Id: I5e2754e5fd462fde132575932e9701ba15bf8028