New feature added and new config item.

Hello - firstly thanks for the module, it has saved us a lot of work!

I hit an issue though on Ubuntu 14.04 PBIS "pbis-open-8.0.0.2016.linux.x86_64.deb.sh" the service name that is configured in the module (lsass) does not match the service that this version seems to install (lwsmd). I made the service name a configurable parameter.

I also added a new variable to the pbis.conf.erb template - namely RequireMembershipOf.

Cheers,
kenzeh