refactoring: replacing ifcfg dependency to storage with one from lib.

Ifcfg is using execCmd from storage.misc module, this patch replaces it
with its equivalent from utils module.

Change-Id: I43b0552e30351c6ae8c3765ab863d1abad750f45
Signed-off-by: Giuseppe Vallarelli <gvallare@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/18217
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>