vboot: add tests for VB2_TRY around screen changes

After these functions are called, no assumptions may be made
about which screen is currently displayed, and thus execution
should return to ui_loop:

- vb2_ui_menu_select
- vb2_ui_screen_back
- vb2_ui_screen_change

When VB2_TRY() is wrapped around these functions, the result
should be returning immediately.  No code following the functions
should be executed.  Add unit test coverage for this.

TEST=make clean && make runtests

Signed-off-by: Joel Kitching <kitching@google.com>
Change-Id: I4fc2a1eb59012eeefce34d25f010a49cb1d957de
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/2721377
Tested-by: Joel Kitching <kitching@chromium.org>
Reviewed-by: Hsuan Ting Chen <roccochen@chromium.org>
Commit-Queue: Joel Kitching <kitching@chromium.org>
2 files changed