Explicitly name element enable-serial-console

We use an element remove-serial-console in image elements.
Renaming this element to match. Also renaming allows us to use
the serial console in devtest runs.
See - https://review.openstack.org/#/c/86272/

Change-Id: I8f1138f58d0046ccdeefa3decc45c36d95c6bf4b

elements/enable-serial-console/README.md

@@ -0,0 +1,10 @@
+Start getty on active serial consoles.
+
+With ILO and other remote admin environments, having a serial console can be
+useful for debugging and troubleshooting.
+
+For upstart:
+  If ttyS1 exists, getty will run on that, otherwise on ttyS0.
+
+For systemd:
+  We dynamically start a getty on any active serial port via udev rules.

elements/serial-console/README.md

@@ -1,10 +1 @@
-Start getty on active serial consoles.
-
-With ILO and other remote admin environments, having a serial console can be
-useful for debugging and troubleshooting.
-
-For upstart:
-  If ttyS1 exists, getty will run on that, otherwise on ttyS0.
-
-For systemd:
-  We dynamically start a getty on any active serial port via udev rules.
+**This element is now deprecated please use enable-serial-console instead**

elements/serial-console/element-deps

@@ -0,0 +1 @@
+enable-serial-console

elements/serial-console/extra-data.d/20-stty

@@ -0,0 +1,5 @@
+#!/bin/bash
+set -uex
+set -o pipefail
+
+echo "Use of serial-console element is deprecated, please use enable-serial-console instead."