bootstd: Add tests for bootstd including all uclasses

Add a set of combined tests for the bootdev, bootflow and bootmeth
commands, along with associated functionality.

Expand the sandbox console-recording limit so that these can work.

These tests rely on a filesystem script which is not yet added to the
Python tests. It is included here as a shell script.

Signed-off-by: Simon Glass <sjg@chromium.org>