kunit: tool: add test for parsing attributes

Add test for parsing attributes to kunit_tool_test.py. Test checks
attributes are parsed and saved in the test logs.

This test also checks that the attributes have not interfered with the
parsing of other test information, specifically the suite header as
the test plan was being incorrectely parsed.

Signed-off-by: Rae Moar <rmoar@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>