simple container tests

* add a simple test script to check everything is ok in container

tests.sh

@@ -0,0 +1,16 @@
+#!/bin/bash -e
+
+cat /etc/os-release
+echo
+
+set -x
+sudo id
+python3 --version
+g++ --version | head -1
+gvim --version | head -1
+xterm -e /bin/bash -c "sleep 1"
+date
+set +x
+
+echo "[OK]"
+