Switch DRBD's rX.res to use /dev/disk/by-id/

[digimer]

If the /dev/sdXY changes, DRBD will fail to attach the backing device. This can happen if a new disk/array is added to the system. Using '/dev/disk/by-id/X' will be more resilient. Find the current '/' host drive and then use that to find the ID during the InstallManifest partition section.

[digimer]

[root@an-a07n01 ~]# df -hP
/dev/sda2        40G  2.8G   35G   8% /
====
[root@an-a07n01 ~]# ls -lah /dev/disk/by-id/scsi-* | grep sda2
lrwxrwxrwx. 1 root root 10 Dec  7 19:28 /dev/disk/by-id/scsi-360030057013c65501f9eec8011d0d46e-part2 -> ../../sda2
====

In this case, the SCSI ID is '360030057013c65501f9eec8011d0d46e', so use:

/dev/disk/by-id/scsi-360030057013c65501f9eec8011d0d46e-part5 (or '-part4' on gpt)