Code review comment for lp:~newell-jensen/maas/rack_register_command

> I had talked to Andres about doing exactly what you are mentioned with
> regards to using InstallSharedSecretScript.run but he said he didn't
> want us to go that route as user interaction for entering the shared
> key doesn't allow automation for using this command. I will run it by
> him and see if he still believes this to be the best route to take on
> this. Thanks for the review.

Fair enough, but both install-shared-secret and this new command are
trivial to automate:

  echo shared-secret | maas-rack register

echo is a builtin in both sh and bash so this avoids revealing the
secret in /proc/*/cmdline.

This isn't just me being paranoid, it's a common practice. PostgreSQL's
psql command, for example, takes a --password flag but it consumes no
arguments; its effect is to force the prompt for a password. It allows
the use of an environment variable, PGPASSWORD, but recommends against
it for security [1].

[1] http://www.postgresql.org/docs/current/static/libpq-envars.html