avoid using PYTHONPATH to enable setup mod hooks, which is problematic for managment command line tool use

- save the directory path to setup mods in /etc/mailinabox.conf
- dynamically add the path to python during hook initialization

ehdd/start-encrypted.sh

@@ -35,5 +35,6 @@ if [ $? -eq 0 ]; then
     ehdd/postinstall.sh || exit 1
 else
     echo "setup/start.sh failed"
+    exit 1
 fi