grub_proc.communicate timeout is too short at 2 seconds

Some VMs I have failed to start on initial boot up of the server with:

"grub-bhyve timed out, please check your grub config."

Even though the timeout in the grub file for the VM is set to 0

If the VM is manually started after FreeNAS is up, there is no problem booting the system.
 

It appears that the 2s second time out is to low and should be a bit higher.

The fix is to change line 280 of:
`/usr/local/lib/python3.7/site-packages/middlewared/plugins/vm.py`

from 2 seconds:
```

```python
try:
    await asyncio.wait_for(self.grub_proc.communicate(), 2)
```

to 5 seconds:

```python
try:
    await asyncio.wait_for(self.grub_proc.communicate(), 5)
```

Could we get this minor change into the next update?