samba-tool: --color=auto looks at stderr and stdout

More often than not we are using colour in stderr, but are deciding
based on stdout's tty-ness. This patch changes to use both, and will
affect the following situation:

 samba-tool  2>/tmp/errors   # used to be colour, now not.

of course, if you want colour, you can always

 samba-tool --color=yes 2>/tmp/errors

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

python/samba/colour.py

@@ -90,7 +90,7 @@ def xterm_256_colour(n, bg=False, bold=False):
     return "\033[%s%s;5;%dm" % (weight, target, int(n))
 
 
-def is_colour_wanted(stream, hint='auto'):
+def is_colour_wanted(*streams, hint='auto'):
     """The hint is presumably a --color argument.
 
     We follow the behaviour of GNU `ls` in what we accept.
@@ -116,13 +116,14 @@ def is_colour_wanted(stream, hint='auto'):
         # Note: per spec, we treat the empty string as if unset.
         return False
 
-    if (hasattr(stream, 'isatty') and stream.isatty()):
-        return True
-    return False
+    for stream in streams:
+        if not stream.isatty():
+            return False
+    return True
 
 
-def colour_if_wanted(stream, hint='auto'):
-    wanted = is_colour_wanted(stream, hint)
+def colour_if_wanted(*streams, hint='auto'):
+    wanted = is_colour_wanted(*streams, hint=hint)
     if wanted:
         switch_colour_on()
     else: