osmo-auc-gen: cmdline help: list algorithms; error messages

In the -h help output, list the names of available algorithms.

In case of option parsing failure, also print help() (so that e.g. for a typo
in the algorithm, the list of algorithms is printed along with the error
message).

If there are -2/-3 or -a missing, show an error message that explains this.

Change-Id: I76732b28d7a553a6293d1707fe398d28b5ef4886
1 file changed