Lock Kubernetes Dashboard version to 2.7.0

- Lock Kubernetes Dashboard version in automated install
- Lock StarlingX ISO version to download on the README instructions

The new Kubernetes Dashboard version (3.0.0) has a breaking change
which is related to its dependencies of nginx and cert-manager.

This commit locks the Kubernetes Dashboard version to 2.7.0, which
corresponds to the Helm Chart version 6.0.8. There's a new Task,
number 48393, to investigate all the changes necessary to allow a
new version of the Kubernetes Dashboard to be used.

Test Plan:

PASS: Verify end-to-end installation for AIO-SX

Closes-Bug: 2027722
Change-Id: I1330a133f344746b791067b1b12c29029be238f5
Signed-off-by: Bruno Muniz <bruno.muniz@encora.com>

virtualbox/pybox/README.md

@@ -145,7 +145,7 @@ will be configured and used.
 4. Grab the latest ISO (this script was last tested with version 8.0.0):
 
     ```shell
-    wget https://mirror.starlingx.cengn.ca/mirror/starlingx/release/latest_release/debian/monolithic/outputs/iso/starlingx-intel-x86-64-cd.iso \
+    wget https://mirror.starlingx.cengn.ca/mirror/starlingx/release/8.0.0/debian/monolithic/outputs/iso/starlingx-intel-x86-64-cd.iso \
       -O $HOME/Downloads/stx-8.iso
     ```
 
@@ -161,7 +161,7 @@ running it):
     python3 ./install_vbox.py \
       --setup-type AIO-SX \
       --iso-location "$HOME/Downloads/stx-8.iso" \
-      --labname StarlingX --install-mode serial \
+      --labname StarlingX --install-mode graphical \
       --config-files-dir ./config/labSetupFiles/ \
       --ansible-controller-config ./config/ansibleFiles/localhost.yml \
       --kubernetes-config-files ./config/kubeFiles/ \
@@ -174,9 +174,9 @@ running it):
 
 The script takes a while to do all the things (from creating a VM and
 installing an OS in it to configuring StarlingX). Several restarts might
-occur, and you might see a VirtualBox with a prompt. You don't need to type
-anything. While the installation script is running it will take care of
-everything for you.
+occur on the VM, and you might see a VirtualBox window with a prompt.
+You don't need to type anything on the VM while the installation script is
+running.
 
 ## Pybox folder structure
 .

virtualbox/pybox/install_vbox.py

@@ -1429,7 +1429,8 @@ def stage_enable_kubernetes(ssh_client):
                 'source /etc/profile && '
                 'cp /etc/kubernetes/admin.conf ~/.kube/config && '
                 'helm repo update; helm repo add kubernetes-dashboard https://kubernetes.github.io/dashboard/ && '
-                'helm install kubernetes-dashboard kubernetes-dashboard/kubernetes-dashboard -f dashboard-values.yaml', timeout=60)
+                'helm install kubernetes-dashboard kubernetes-dashboard/kubernetes-dashboard '
+                '-f dashboard-values.yaml --version 6.0.8', timeout=60)
 
     if exitcode == 0:
         LOG.info("###### Creating an admin-user service account with cluster-admin provileges ######")