Fixing a few goofs from ac5de466
Added dhcp_service_name method to determine proper dhcpd service name to use in restart during sync
Added ubuntu to kickstart_start snippet and one more instance in kickstart_done
Volume groups can have hyphens too.

If a VG has a hyphen in the name, partition_location will not have the
correct path. Must escape hyphens there too.
(issue#407) Enable authn_passthrough for Cobbler Web

There is currently no support for kerberos single sign-on in cobbler web.
This patch allows apache or another web server to set the REMOTE_USER variable which
will be used as the authenticated user for cobbler API authorization calls
Fixed issue with MAC address verification

- Removed errant ':' systems from the last two octet matches
- Added checks that the string does not start or end with extra characters
Refactor function cobbler.utils.is_mac

Use a precompiled and faster regular expression and add more tests.
timeit with 64M iterations: 48.32 versus 42.38 seconds.
Speedup function cobbler.utils.is_mac

Use both lower case and upper case hexadecimal digits in the regex
instead of using the re.IGNORECASE option. Also add more tests.
timeit with 64M iterations: 42.78 versus 39.74 seconds.