Configure plugins by name

To configure core plugin or service plugins, instead of using class
names, simpler names can also be used.

Example:
service_plugins = router, firewall, lbaas
core_plugins = linuxbridge

It is a new feature brought in Icehouse (thanks to stevedor): http://git.io/QfyiLw
Bringing it into puppet-neutron simplifies the parameters use for end-user.

Change-Id: Ib96cc8ea67e89c37226ee6b9d1ae811fa1507672
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>
Merge "Configure plugins by name"