Respect NO_COLOR environment variable

configuration/cdist.cfg.skeleton

@@ -17,6 +17,8 @@
 #     Use a colored output for different log levels.
 #     It can be a boolean or 'auto' (default) which enables this feature if
 #     stdout is a tty and disables it otherwise.
+#     Colored output is always disabled if the NO_COLOR environment variable is
+#     defined (https://no-color.org/).
 # colored_output = auto
 #
 # conf_dir
@@ -51,7 +53,7 @@
 #
 # out_path
 #     Directory to save cdist output in.
-# out_path = 
+# out_path =
 #
 # parallel
 #     Process hosts in parallel. If -1 then the default, number of CPU's in
@@ -77,6 +79,6 @@
 # remote_shell = /bin/sh
 #
 # verbosity
-#     Set verbosity level. Valid values are: 
+#     Set verbosity level. Valid values are:
 #     ERROR, WARNING, INFO, VERBOSE, DEBUG, TRACE and OFF.
 # verbosity = INFO