Follow up to: e0d3313
- Revert renames from `encrypted` and `encrypted_file` back to `credentials`.
They might be using our Encrypted* generators but from that level of abstraction
they're still about credentials.
- Same vein: extract a `credentials` method for the `encrypted` local variable. But
don't call it `encrypted` just because it uses that under the hood. It's about
capturing the credentials. It's also useful in `change_credentials_in_system_editor`.
- Remove lots of needless argument passing. We've abstracted content_path and key_path
into methods for a reason, so they should be used. Also spares a conspicuous rename
of content_path into file_path in other methods.
- Reorders private methods so they're grouped into: command building blocks, option
parsers, and the generators.
- Extracts commonality in the credentials application tests. A tad unsure about this.
But I do like that we go with key, content thus matching the command and remove the
yield which isn't really needed.
- Moves test/credentials_test.rb to beneath the test/application directory. It's a
Rails application test, so it should be in there.
- Uses `root.join` — a neat trick gleaned from the tests! — and composes the configuration
private methods such that the building block is below the callers.
