Change code coverage to write to app data folder rather than sdcard.

The InstrumentationTestRunner would previously write code coverage data to the sdcard. With the recent SDCARD_WRITE permission addition, generating code coverage would fail if test app did not declare the SDCARD_WRITE permission. This CL changes InstrumentationTestRunner so by default, the coverage data is saved to the app's private data folder. At the test run conclusion it outputs the path to this file so runtest or another test harness find the path to the coverage file.