BZ #1054181 - Set OS description consistently, install LSB

OS descriptions are filled in by LSB, which relies on lsb_release (supplied by
redhat-lsb-core).  On RHEL, they usually contain the variant string "Server",
so also update the description we preset to match that supplied by lsb_release.
Merge pull request #104 from domcleal/1054181-branding

BZ #1054181 - Set OS description consistently, install LSB