cluster: fix api breakage related to suicide

Fix inadvertent v0.11 changes to the definition of suicide, particularly
the relationship between suicide state, the disconnect event, and when
exit should occur.

Workers shouldn't normally exit on disconnect, it doesn't give them time
to do a graceful finish of open client connections. But on unexpected
disconnect they should exit so the workes aren't left around after the
master.
!fixup emit 'setup' in nextTick