test-terminal-util: print value of colors_enabled()

This makes it easier to diagnose why colors are disabled.

src/test/test-terminal-util.c

@@ -25,6 +25,10 @@
         "in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat " \
         "non proident, sunt in culpa qui officia deserunt mollit anim id est laborum."
 
+TEST(colors_enabled) {
+        log_info("colors_enabled: %s", yes_no(colors_enabled()));
+}
+
 TEST(default_term_for_tty) {
         puts(default_term_for_tty("/dev/tty23"));
         puts(default_term_for_tty("/dev/ttyS23"));