CI/molecule: use common vars as well and simplify run (#13520)

The molecule_run.sh isn't really needed since the switch to gitlab-ci
matrix runs.

Also use the inventory variables pattern for kata-containers.

tests/scripts/molecule_run.sh

@@ -1,34 +0,0 @@
-#!/bin/bash
-set -euxo pipefail -o noglob
-
-export LC_ALL=C.UTF-8
-export LANG=C.UTF-8
-
-_PATH='roles'
-_EXCLUDE=""
-
-while [[ $# -gt 0 ]] ; do
-    case $1 in
-        -e|--exclude)
-            _EXCLUDE="${_EXCLUDE} -not -path ${_PATH}/$2/*"
-            shift
-            shift
-            ;;
-        -i|--include)
-            _PATH="${_PATH}/$2"
-            shift
-            shift
-            ;;
-        -h|--help)
-            echo "Usage: molecule_run.sh [-h|--help] [-e|--exclude] [-i|--include]"
-            exit 0
-            ;;
-    esac
-done
-
-for d in $(find ${_PATH} ${_EXCLUDE} -name molecule -type d)
-do
-    pushd $(dirname $d)
-    molecule test --all
-    popd
-done