The VIR_STORAGE_POOL_EVENT_REFRESHED constant does not
reflect any change in the lifecycle of the storage pool.

It should thus not be part of the storage pool lifecycle
event set, but rather be a top level event in its own
right. Thus we introduce VIR_STORAGE_POOL_EVENT_ID_REFRESH
to replace it.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

Add storage event handling infrastructure to storage_event.[ch], following
the network_event.[ch] pattern.