This supports specifying a file system path to test(s) to run. The path can be
a java test class file, a java package directory, or a parent directory
containing many tests.
This change allows users to run tests independently from test_defs.xml.
BUG 2133198
With this change, also refactored runtest as follows: Modified the
test suite schema and python implementation to have an inheritance
structure. Each test type has its own python module, which will
also handle the logic of running the test.
