Move allowvssprovider=false to vm-data field

Currently we're setting allowvssprovider=false in the other-config
field. However, this setting is not honored in the other-config field,
allowing vss-based snapshots to be created.

The allowvssprovider=false should be moved to the vm-data field in
xenstore as that field is used to decide whether vss snapshotting is allowed or not.

Amended to change: 'str(False)' to 'false'.

Relevant code:

https://github.com/openstack/nova/blob/master/nova/virt/xenapi/vm_utils.py#L233

Manually set allowvssprovider=false in the vm-data field:

xe vm-param-set uuid=<VM-UUID> xenstore-data:vm-data/allowvssprovider=false

References:

https://github.com/mcclurmc/xcp-storage-managers/blob/master/drivers/vss_control#L38
https://github.com/mcclurmc/xcp-storage-managers/blob/master/snapwatchd/snapwatchd#L298

Change-Id: I96efbc18cb7eb0ee2d0e6526b3c4f3502a68e1dd
Fixes: bug #1112673
Merge "Move allowvssprovider=false to vm-data field"