CA-121481: /dev/root does not exist at installation time

sm-multipath was meant to start at run time only.
We use this function to fix boot from SAN at installation time, too.
We cannot rely on /dev/root so we borrowed some utility functions
from dracut with a slight modification

Signed-off-by: Germano Percossi <germano.percossi@citrix.com>
Signed-off-by: Frediano Ziglio <frediano.ziglio@citrix.com>