Fix compatibility with DRBD 8.3

DRBD 8.3 changes two more things compared to 8.2:
  - /proc/drbd format changed in multiple ways; the part we're
    interested is the ‘st:’ to ‘ro:‘ change (in the changelog named as
    “Renamed 'state' to 'role'”
  - “drbdsetup /dev/drbdN show” changed the ‘device’ stanza from:
      device "/dev/drbd0";
    to:
      device                  minor 0;

This patch fixes these both and adds data files and unittests for DRBD
8.3.1.

Signed-off-by: Iustin Pop <iustin@google.com>