cmdlib: Work around race condition in DRBD before version 8.0.13

DRBD goes into sync mode for a short amount of time after
executing the "resize" command. DRBD 8.x below version
8.0.13 contains a bug whereby calling "resize" in sync
mode fails.

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