Tools: hv: vssdaemon: skip all filesystems mounted readonly

Instead of making a list of exceptions for readonly filesystems
in addition to iso9660 we already have it is better to skip freeze
operation for all readonly-mounted filesystems.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Acked-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>