samba-tool: make --color a general option

We don't put --color into options.SambaOptions because we can't handle
the 'auto' case in the options module without knowing whether or not
self.outf is a tty, and a) this might not be resolved and b) is fiddly
to pass through.

The .use_colour class flag allows samba-tool subcommands to avoid having
--color, and is *also* useful in the short term for visualise and drs
commands to avoid having this --color clobber their own bespoke versions
(temporarily, during the transition).

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>

python/samba/netcmd/visualize.py

@@ -92,6 +92,7 @@ class GraphCommand(Command):
     }
     takes_options = COMMON_OPTIONS + DOT_OPTIONS
     takes_args = ()
+    use_colour = False
 
     def get_db(self, H, sambaopts, credopts):
         lp = sambaopts.get_loadparm()