Feature request: let the user turn syzkaller off for one of VMs

[ramosian-glider]

When I'm running syzkaller on two adb devices, I may want to reproduce some crashes on one of them, while still continuing to fuzz the second one, but do not want to restart the master.

It would be nice to have a possibility to temporarily exclude a device from the fuzzing process.

[dvyukov]

The general plan is that syz-manager should reproduce and minimize crashers on its own without any manual work.
This feature is somewhat difficult to incorporate into syz-manger logic. It is complex enough already and the feature makes sense only for adb. Perhaps we could hack vm/adb to check presence of some magic file with adb device id and don't try to connect to that device while the file is there...

[dvyukov]

syz-manager now reproduces crash automatically.