GitLab

1. Added test runners for the two accessibility sets of tests
   to the cts-tradefed test types. While these runners are
   specific to the accessibility tests, the CTS maintainers
   are fine adding specific tests to the CTS tradefed library
   since there is already such a precedent and it is not common
   for someone to need adding custom runners.

2. Modified the build rule for a CTS package to take as an
   argument a runner class name. This enabled the package to
   specify which runner to invoke the tests in it.

3. Added tests for the accessibility API to maximize CTS test
   coverage. Currently not tested are interfaces and callbacks
   invoked by the system.

5. The accessibility tests can be used as an example for writing
   tests that require modification of the secure settings or
   generally require execution of shell commands from the host
   before and after running the tests.

bug:5946699

Change-Id: I3b68bff4fed846b374a88a2abe812801bd6f2c8f