Add fedora/el-7 systemd support

This updates the packaging and adds a systemd service file
and supporting files to support systemd on Fedora >= 18 and
EL >= 7.

In addition to the razor-server.service file itself, the
razor-server-tmpfiles.conf used the systemd tmpfiles.d
mechanism to ensure that the /run/razor-server
directory is created on boot with the proper ownership
as /run is now using tmpfs.

The /usr/share/razor-server/razor-server.env file
simply wraps up environment variables that were
being set in the init script in a form suitable
for systemd.