[rotorcraft] allow to turn off motors in failsafe mode

Allow arming/disarming motor as long as not in KILL mode and ahrs is aligned.
[modules] nav_survey_poly_osam: sweep improvements

Added half U-turn even if not sweepback
Some modification to change sweep distance and number of points using telemetry parametrers
option to use default 1/2 sweep distance for start line or using alternative 1/32 sweep start

Its is very useful when using poligon survey osam for photogrametry

see #938