[libvirt] [PATCH 0/8] Refactor event state handling to fix crash

When running while true ; do date ; ../tools/virsh -q -c test:///default 'shutdown test; undefine test; dominfo test' ; done we often experiance hangs or crashes or memory corruption in glibc. The reason is that when the virConnectPtr is free'd this in turn frees the event state, which in turn unregisters the event timer. The timer may, however, still fire one last time and it is possible this occurs after the event state has been freed. The solution in this series is to only register the timer when the first callback is added and unregister the timer, when the last callback is removed. In doing this patch, I decide to unify more of the event handling across drivers, and simplify the API usage by drivers, and hide all the impl details.