update create-image.sh to fail early

create-image.sh

@@ -8,7 +8,17 @@ IMAGE_NAME="${APPLIANCE_NAME}-$(TZ='UTC' date +%Y.%m.%d-%H%M%S).raw"
 COMPRESSED_IMAGE_NAME="${IMAGE_NAME}.zst"
 
 if [[ ${EUID} -ne 0 ]]; then
-    >&2 echo "ERROR: Please run this script as root"
+    >&2 echo "$0: error: Please run this script as root"
+    exit 1
+fi
+
+if ! command -v appliance-creator > /dev/null; then
+    >&2 echo "$0: error: unable to find command 'appliance-creator'"
+    exit 1
+fi
+
+if ! command -v shasum > /dev/null; then
+    >&2 echo "$0: error: unable to find command 'shasum'"
     exit 1
 fi