Locked VM state after disk full message

[CaptainFlint]

Consider the situation when there is low disk space on the partition with virtual machines.

1. Start a VM with dynamic hard disk and make it use the unused space so that the disk image grew in size (e.g. create a new VM and start installing an OS into it).
2. When host partition is filled, VB shows a warning about full disk and pauses the mavhine.
3. Close the VM window; when asked about action, select "Save state".
4. VB shows a message that saving state operation failed because of insufficient disk space.

Now VM session is permanently locked in "saving" state and can be neither powered off, nor saved, nor unpaused. It can only be killed from a task manager.

[CaptainFlint]

Log file of the test VM

[wacher]

I think, this is duplicate of #6189.