AI 144340: Added support to run native tests on the device.

AI 144340: Added support to run native tests on the device.
  The tests name must start with 'test_'.
  Tests should return 0 on success, 1 on failure.
  * development/testrunner/test_defs.xml:
  Added new element to represent native tests.
  * development/testrunner/test_defs.py:
  Added handling of the new <test-native> element.
  The testsuite has new IsNative method.
  TestDefinition's iterator is ordered by test names.
  Added GetDescription() method to access the optional description.
  * development/testrunner/runtest.py:
  Print the description next to the test name if applicable
  (runtest_py -l)
  Added a _RunNativeTest method to run a test on the target, report
  the status and clean up the test after the run.
  Added
  BUG=1601432

Automated import of CL 144340