Create tgz archive also when only db is backup'ed

There should always be created an archive when running the backup script
succesfully. 
It is not clear for a user that if he uses the --skip-fs option he needs to look
into the $BASE dir to find a file named database.sql.

Creating a tgz file for all types of backup. To allow the user to see what the
backup contains, the "skip-db" and "skip-fs" changes the filename for the
resulting archive. This allows the user to se if he can recreate his TYPO3
installation from the given backup file.
Delete the database dump at the end if it has been created.