Instead of having individual counters n_serializing and n_deserializing
have a single one n_reloading, which should be sufficient.
Set n_reloading when we are about to go down for reexecution to avoid
cgroup trimming when we free the units for reexecution.
We simply keep open copies of the dbus connections across the
reexecution and close them as last step of it. A client can thus simply
wait until its connection is dropped to know when the reexecution is
finished.
https://bugzilla.redhat.com/show_bug.cgi?id=698198
