Px4-autopilot: High sensor noise in SITL when disarmed

[julianoes]

I realized that in SITL Gazebo (using standard_vtol) the sensor noise (especially accel) is quite high.

In my opinion this is far from reality and should be improved.

I stumbled upon this in SDK tests where arming failed with the message:

[commander] Preflight Fail: Accel Range, hold still on arming

https://logs.px4.io/plot_app?log=01919d08-3298-45ff-8cb2-c99929b890ca

@bresch also saw it in SITL CI.

[LorenzMeier]

I'm making this a release broker since it will induce SITL flakyness that should not be in a release.

[julianoes]

So while we don't scale noise with motor speeds or the fact that we're armed, this actual issue seems to be caused by the standard_vtol bouncing on the ground or somehow interacting with it.

[julianoes]

I'll push a fix tomorrow, I've managed to get the standard_vtol less jittery and added somewhat proper airspeed noise.