Fix Admin CLI usage info

[wajda]

Currently running Admin CLI with --help prints this:

Usage: Spline Admin CLI [db-init|db-upgrade|db-exec] [options] <args>...

It should print a correct usage example depending if it is run as a Java command or a disposable docker container. E.g.:

Usage: docker run -it --rm [db-init|db-upgrade|db-exec] [options] <args>...
- or -
Usage: java -jar admin-X.Y.Z.jar [db-init|db-upgrade|db-exec] [options] <args>...