plugin: New role settings system
Roles can now require changes to MW-Vagrant settings by defining them in
puppet/modules/role/settings/<role>.yaml. The value of each will
either be absolute or relative to the current value, depending on each
setting's combiner definition.
Role settings are shown to the user when viewing the role documentation
(vagrant roles info) and when enabling or disabling the role. The
latter will also trigger a reload upon the next provision.