Support for Cisco ML2 Mech Driver

Partially Implements: blueprint support-ml2-nexus-driver

Change-Id: I5e0486c9db22abfcbab205e6f57bbafe8f0b5dd4
Undeprecate enable_security_group parameter

Introduced by commit f87e7d964c19cc2be33226df66f0c823af993d49
in Neutron 2014.1.rc1, this config is far from deprecated.

Restore it with proper default value.

Change-Id: If74658dbdb0fc1961a664df7484ebc2d1b0a118b
Merge "Support for Cisco ML2 Mech Driver"
Merge "Undeprecate enable_security_group parameter"
Add network_device_mtu to neutron.conf

Already a parameter for L3_agent, but that isn't
exactly the right configuration, due to the fact
that this parameter is specifically a L2 feature.

Added in neutron.conf to set the default MTU for all
created networks. Discussion available here:

http://lists.openstack.org/pipermail/openstack-dev/2013-October/017033.html
https://bugs.launchpad.net/openstack-manuals/+bug/1242534

Added test to validate parameter
Fixed mis-spelled parameter in test
Added deprecation warninigs to agents/l3.pp

Closes-Bug: #1329643
Change-Id: Id8544799855c500f0c871681695db502ab4dc87c
Merge "Add network_device_mtu to neutron.conf"