rosie create: test battery

Add test battery for `rosie create`.

* Test bad info file with `--info-file=FILE`.
* Test empty answer in interactive mode.
* Test with good `--info-file=FILE`.
* Test normal mode with mock editor.
* Test no checkout mode.

Allow `owner` (in `rose-suite.info`) to have a default value other than the current user by supporting the `[rosie-id]prefix-owner-default.PREFIX` setting in `$HOME/.metomi/rose/conf`.

Resolve part of #78.