bdev: allow ignoring of size in Assemble()

This patch changes the DRBD8 class (the only one to use the size in
Assemble) to ignore the size in Assemble when a zero size is passed.
This will allow activation of disks even when the size recorded in the
configuration is wrong.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>

lib/bdev.py

@@ -1129,9 +1129,10 @@ class DRBD8(BaseDRBD):
     """
     args = ["drbdsetup", cls._DevPath(minor), "disk",
             backend, meta, "0",
-            "-d", "%sm" % size,
             "-e", "detach",
             "--create-device"]
+    if size:
+      args.extend(["-d", "%sm" % size])
     result = utils.RunCmd(args)
     if result.failed:
       _ThrowError("drbd%d: can't attach local disk: %s", minor, result.output)