Assertion atomic_complete_pending failed after EBUSY on hotplug
I start Weston/DRM/GL with three monitors connected.
Unplug one monitor, and re-plug it. This hits EBUSY, which is likely #24.
Unplug the same monitor again, and re-plug it. That results in
weston: ../../git/weston/libweston/backend-drm/kms.c:1404: atomic_flip_handler: Assertion `output->atomic_complete_pending' failed.