Debian: stx-init-env: fix --nuke option KeyError exception

Add the checking for minikube_exists to avoid the KeyError error,
when the command './stx-init-env --nuke' is executed and the minikube
cluster doesn't exist.

Story: 2009897
Task: 45824

Test Plan:
Pass: export MINIKUBENAME=abc ......
      './stx-init-env --nuke' works without the KeyError exception.

Signed-off-by: Zhixiong Chi <zhixiong.chi@windriver.com>
Change-Id: I2cf46e01df312604ca2a0afa38a498e7397747b8

stx-init-env

@@ -61,6 +61,8 @@ minikube_exists() {
     local script=$(cat <<'END'
 import json,sys
 data = json.load (sys.stdin)
+if 'valid' not in data or 'invalid' not in data:
+    sys.exit(1)
 for x in data['valid']+data['invalid']:
     if x['Name'] == sys.argv[1]:
         sys.exit(0)
@@ -218,6 +220,10 @@ if [ "$STX_PLATFORM" = "minikube" ]; then
         if minikube_exists ; then
             notice "Deleting minikube cluster \`$MINIKUBENAME'"
             $MINIKUBE delete -p "$MINIKUBENAME" || exit 1
+        else
+            notice "Please check your minikube cluster MINIKUBENAME: \`$MINIKUBENAME'."
+            notice "It doesn't exist or it existed but not for your MINIKUBE_HOME: \`$MINIKUBE_HOME'."
+            notice "Please re-export the correct project variable pairs!!!"
         fi
         exit 0
     fi