Align miniboot.cfg with recent kickstart.cfg changes

Incorporate the following commits into miniboot.cfg:
- https://review.opendev.org/c/starlingx/metal/+/857894
- https://review.opendev.org/c/starlingx/metal/+/862669

The current redfish installs are broken because the sysadmin user
is no longer properly setup for password-change required on first login.
This commit pulls in the required change from kickstart.cfg.

Test Plan:

PASS:
- Verify that the sysadmin/sysadmin password is required to change
  on first login via sushy boot
- Verify unsuccessful installation in sushy emulator without this fix
- Verify successful installation in sushy emulator with this fix
- Verify the FD deletion error is no longer present

Story: 2010118
Task: 46714

Signed-off-by: Kyle MacLeod <kyle.macleod@windriver.com>
Change-Id: I1c39184c05442946b55ec375e643e94e6dc89fd6

kickstart/files/miniboot.cfg

@@ -871,7 +871,15 @@ export prefix=""
 # Assume there is no Platform Backup (persistent) Partition
 export BACKUP_PART_FOUND=0
 
-export STOR_DEV_FDS="$(ls -1 /proc/$$/fd | egrep -v "^(0|1|2|255)$" | xargs)"
+export STOR_DEV_FDS=""
+
+export PROC_SELF_FDS="$(ls -1 /proc/$$/fd | egrep -v "^(0|1|2|255)$" | xargs)"
+for fd in ${PROC_SELF_FDS}; do
+    export realpath=$(readlink -f /proc/$$/fd/"${fd}")
+    if [ -e "${realpath}" ]; then
+        STOR_DEV_FDS="${STOR_DEV_FDS} ${fd}"
+    fi
+done
 
 ##########################################################################
 #                     Local Kickstart variables                          #
@@ -2007,6 +2015,29 @@ true
 
 ###########################################################################
 
+%post --interpreter=/bin/bash
+HOOK_LABEL="post"
+. /tmp/lat/ks_functions.sh
+ilog "*********************************************************"
+ilog "****    Post - Add user/groups                         **"
+ilog "*********************************************************"
+# Set password for root to 'root'
+usermod -p '$6$hEv/K.fPeg/$ezIWhJPrMG3WtdEwqQRdyBwdYmPZkqW2PONFAcDd6TqWliYc9dHAwW4MFTlLanVH3/clE0/34FheDMpbAqZVG.' root
+
+# Remove admin user whether it exists or not
+deluser admin || true
+
+# Create the sysadmin user
+useradd sysadmin -m --shell /bin/bash -G sudo --password 4SuW8cnXFyxsk
+chage -d 0 sysadmin
+
+# add 'nobody' group
+groupadd nobody
+
+# Reload /etc/group- to make systemd-sysusers.service happy
+/usr/sbin/grpconv || report_failure_with_msg "Failed to convert from shadow passwords and groups"
+%end
+
 %post --interpreter=/bin/bash
 HOOK_LABEL="post"
 . /tmp/lat/ks_functions.sh