Preflight HOVER_PID w/ throttle

Pre-test flight HOVER_PID mode with hover throttle enabled.
First throttle tuning attempt

Changed minimum divergence throttle to 50% (instead of 40%) and changed
sink rate range to +_ 1 m/s (instead of +-2).  Didn't work, the plane
just kept climbing
Second throttle tuning attempt

Reset divergence throttle limits back to original values (preflight)
because airplane could not stop climbing when in hover mode.  Means
trouble with first flight was probably due to bad PID gains (most likely
wrong k_i or I_max values)