05core: print warnings to secondary consoles

This allows us to print the helpful messages that we have added
for our users before they enter dracut's emergency shell to all
configured consoles on the machine.

Closes coreos/fedora-coreos-tracker#954

overlay.d/05core/usr/lib/dracut/modules.d/99emergency-shell-setup/emergency-shell.sh

@@ -64,13 +64,15 @@ EOF
             echo "Displaying logs from failed units: ${failed}"
             for unit in ${failed}; do
                 # 10 lines should be enough for everyone
-                journalctl -b --no-pager --no-hostname -u ${unit} -n 10
+                SYSTEMD_COLORS=true journalctl -b --no-pager --no-hostname -u ${unit} -n 10
             done
         fi
     fi
 }
 
-# If we're invoked from a dracut breakpoint rather than
-# dracut-emergency.service, we won't have a controlling terminal and stdio
-# won't be connected to it. Explicitly read/write /dev/console.
-_display_relevant_errors < /dev/console > /dev/console
+# Print warnings/informational messages to all configured consoles on the
+# machine. Code inspired by https://github.com/dracutdevs/dracut/commit/32f68c1
+MESSAGE="$(_display_relevant_errors)"
+while read -r _tty rest; do
+    echo -e "$MESSAGE" > /dev/"$_tty"
+done < /proc/consoles