use uuid to mount root partition

use uuid to mount root partition

Some servers assign different device labels in the installer
and firstboot which causes the boot process to break.  For example
sometimes a virtual cd might be /dev/sda during intstall, but not
be present after the reboot so now the root drive is /dev/sda.
Mounting by uuid will allow the boot to work even if the device labels
change between boots.

Signed-off-by: davidplunkett <dp7642@att.com>
Change-Id: I82025fc69285418bae48b7b32d31d3e1a0552cbb