Fix failure to set instdev parameter when we use ks-setup.cfg

When we create the prestage iso with an external script,
ks-setup.cfg, we may not provide the rootfs_device or
boot_device parameter. This is a valid scenario where these
parameters are defined in ks-setup.cfg. An installation failure
is observed in this case.

The cause of the failure is that the prestage code is handled in
a pre-part hook. This commit moves it to a ks-early hook.

In this commit, a provision for the execution of a custom script
named ks-addon.cfg is also made. This script is a bash script
that must execute in the last post hook.

Test Plan:
PASS: Verify that the installation succeeds when the rootfs
      and boot device parameters are only specified via
      the ks-setup.cfg.

PASS: Verify that the external script, ks-addon.cfg, is executed
      after the install and configurations are done.

PASS: Verify that the logs from the execution of ks-addon.cfg
      are present in kickstart.log.

Closes-bug: 1997305

Signed-off-by: Shrikumar Sharma <shrikumar.sharma@windriver.com>
Change-Id: Ica1735aef3ab457cf0609ebee6aac45671e97987

kickstart/files/kickstart.cfg

@@ -971,8 +971,8 @@ true
 # This code is only executed if "prestage" is set in the command line
 # to the kernel.
 
-%pre-part --interpreter=/bin/bash
-HOOK_LABEL="pre-part"
+%ks-early --interpreter=/bin/bash
+HOOK_LABEL="ks-early"
 . /tmp/lat/ks_functions.sh
 
 # First, parse /proc/cmdline to find the boot args
@@ -989,8 +989,6 @@ if check_prestage -eq 0 ; then
 
     mkdir -p ${ISODIR}
 
-    rootfs_device=${INSTDEV}
-
     # Mount the isofile
     mount "${ISO_DEV}" "${ISODIR}"
     rc=$?
@@ -1006,6 +1004,7 @@ if check_prestage -eq 0 ; then
 
     # override the INSTDEV based on the information from ks-setup.cfg
     export INSTDEV="${rootfs_device}"
+    export instdev="${rootfs_device}"
 
     ilog "rootfs device is ${INSTDEV}"
 
@@ -3090,5 +3089,14 @@ if [ "${storage}" = true ] ; then
     ln -s /usr/share/starlingx/pmon.d/syslog-ng.conf ${IMAGE_ROOTFS}/etc/pmon.d/syslog-ng.conf
 fi
 
+if [ -e "/instboot/ks-addon.cfg" ]; then
+    ilog "Running kickstart addon script"
+    source /instboot/ks-addon.cfg
+    rc=$?
+    if [ "${rc}" -ne 0 ]; then
+        ilog "Addon script ks-addon.cfg  exited with [rc=${rc}]"
+    fi
+fi
+
 true
 %end