Unify a few re.compile calls in DRBD

These are both cleanups and, in the case of _MassageProcData, switching
from a weaker RE to a stronger one (we now need cs: in the line,
previosuly any line starting with \d+: was accepted).

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>