ejabberdctl: Use $INSTALLUSER's home directory

Make sure ejabberdctl uses the $INSTALLUSER's .erlang.cookie file even
if the script was executed by root.
ejabberdctl: Create home directory as root

If the $INSTALLUSER is not root, he will usually not have the necessary
permissions to create his home directory.
ejabberdctl: Remove outdated comment

The home directory is no longer set to $SPOOL_DIR.
Merge pull request #263 from weiss/fix-ejabberdctl-issues

Fix ejabberdctl issues