Fix creation of plain instances with --no-wait-for-sync

As reported on the devel mailing list by Christos Stavrakakis,
creation of plain instances is broken when the --no-wait-for-sync flag
is passed, because in that case WaitForSync is not called, hence
SetDiskID is not called at all, resulting in a None physical_id being
passed to backend.

We fix that by explicitly calling SetDiskID, which will cover the
pause/resume and os_add RPC calls.

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

lib/cmdlib.py

@@ -10138,6 +10138,11 @@ class LUInstanceCreate(LogicalUnit):
     _ReleaseLocks(self, locking.LEVEL_NODE_RES)
     if iobj.disk_template != constants.DT_DISKLESS and not self.adopt_disks:
+      # we need to set the disks ID to the primary node, since the
+      # preceding code might or might have not done it, depending on
+      # disk template and other options
+      for disk in iobj.disks:
+        self.cfg.SetDiskID(disk, pnode_name)
       if self.op.mode == constants.INSTANCE_CREATE:
         if not self.op.no_install:
           pause_sync = (iobj.disk_template in constants.DTS_INT_MIRROR and