test/py: add test of basic shell functionality

This tests whether the following features of the U-Boot shell:
- Execution of a directly entered command.
- Compound commands (; delimiter).
- Quoting of arguments containing spaces.
- Executing commands from environment variables.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Simon Glass <sjg@chromium.org>
2 files changed