Add test cases for'PMA_Error::getBacktrace()'.

Signed-off-by: Dhananjay Nakrani <dhananjaynakrani@gmail.com>
TESTING:Add test case 'sendErrorReports != never' for 'testGetDispErrorsForDisplayFalse()'.

Signed-off-by: Dhananjay Nakrani <dhananjaynakrani@gmail.com>