CA-115733:VM(with dynamic memory) memory changes every few seconds on it own

This case is caused by some VM was stuck and cannot change memory allocation. In this case. DMC will give the redundant memory (which is prepare to give to stuck one) to other VMs.

But in next iteration of balloon, the stuck VM still counted to DMC and trying to balancing the memory allocation in VMs. Which will cause the VM who get the redundant memory last time hand in the memory. In XenCenter, you will find some VM memory changes every few seconds.

The solution here is to mark the VM as cannot ballooning if it has been marked as stuck. It is solution to VM stuck problem on XAPI part and will not solve the stuck problem on VM.  There still need some work to do to check why the VM stuck.

Signed-off-by: Cheng Zhang <cheng.zhang@citrix.com>