Mix of --<option> and -<option>

The output of `gh-ost --help` shows short options like `-database` in go-style.
However `gh-ost` without options shows `2016-08-03 09:16:34 FATAL --database must be provided and database name must not be empty` with `--database` instead.

Let's settle for the go-style one-dash options instead of the GNU style long options.
This prevents the later use Unix style short options, but that should be fine