contrib/check-config: conditionally disable color output.

Redirecting check-config.sh output to a file puts control character
output into that file, which isn't helpful for reading.

Disable colorized output if either
1. NO_COLOR environment is set to "1"
2. stdout is not a terminal.

Signed-off-by: Scott Moser <smoser@brickies.net>

contrib/check-config.sh

@@ -25,6 +25,10 @@ if ! command -v zgrep > /dev/null 2>&1; then
 	}
 fi
 
+useColor=true
+if [ "$NO_COLOR" = "1" ] || [ ! -t 1 ]; then
+	useColor=false
+fi
 kernelVersion="$(uname -r)"
 kernelMajor="${kernelVersion%%.*}"
 kernelMinor="${kernelVersion#$kernelMajor.}"
@@ -41,6 +45,10 @@ is_set_as_module() {
 }
 
 color() {
+	# if stdout is not a terminal, then don't do color codes.
+	if [ "$useColor" = "false" ]; then
+		return 0
+	fi
 	codes=
 	if [ "$1" = 'bold' ]; then
 		codes='1'