samba-tool: Correct handling of default value for use_ntvfs and use_xattrs

samba-tool: Correct handling of default value for use_ntvfs and use_xattrs

Because these options are optional based on build-time rules, we need to encode the
default value from the additonal Option() blocks in the run() declaration.

Then we can correctly check only for the expected options, and not inconsistently for
None (causing classicupgrade to fail).

BUG: https://bugzilla.samba.org/show_bug.cgi?id=12543
Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Garming Sam <garming@catalyst.net.nz>