AutoTest: print failed copter test

Name of the failed tests appears at the moment it fails and then again
after all tests have been run.  This hopefully makes it slightly easier
to know which test has failed
Copter: init pos_control z-axis after setting speed and accel
AC_WPNav: init_loiter sets speed, accel before calcing stopping distance

The stopping distance depends upon the speed and acceleration so these
must be updated first
AC_PosControl: add set_target_to_stopping_point_xy method

Fixed bug in get_stopping_point_xy in which it would update Z-axis
target if vehicle was moving less than 10cm/s horizontally
Copter: disable RALLY points by default

This saves 2k of flash which allows the code to fix on the APM1/2