summary_tests.py: Move resultsfiles function to utils

This is going to be needed in core_tests, so lets put it in the shared
module.

Signed-off-by: Dylan Baker <baker.dylan.c@gmail.com>
core_tests.py: Add tests for load_results_folder

Signed-off-by: Dylan Baker <baker.dylan.c@gmail.com>
core_tests.py: Add tests for TestResult

Specifically TestResult should convert a 'result' value into a
status.Status derived object.

Signed-off-by: Dylan Baker <baker.dylan.c@gmail.com>