Tools: hv: vssdaemon: Ignore VFAT mounts during the Freeze operation

If the guest has a FAT file system mounted, skip it during the FREEZE
operation. With this change we can support host initiated backup of
the guest even when the guest may have FAT file systems mounted.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>