Fixed HDF5 bug with event based starting from ruptures (--hc)

[micheles]

In large calculations I was getting the error

  File "/home/michele/oq-engine/openquake/commonlib/datastore.py", line 542, in __contains__
    return key in self.hdf5 or self.parent and key in self.parent.hdf5
  File "h5py/_objects.pyx", line 54, in h5py._objects.with_phil.wrapper
  File "h5py/_objects.pyx", line 55, in h5py._objects.with_phil.wrapper
  File "/home/michele/openquake/lib64/python3.10/site-packages/h5py/_hl/group.py", line 483, in __contains__
    return self._e(name) in self.id
  File "h5py/h5g.pyx", line 466, in h5py.h5g.GroupID.__contains__
  File "h5py/h5g.pyx", line 467, in h5py.h5g.GroupID.__contains__
  File "h5py/_objects.pyx", line 54, in h5py._objects.with_phil.wrapper
  File "h5py/_objects.pyx", line 55, in h5py._objects.with_phil.wrapper
  File "h5py/h5g.pyx", line 540, in h5py.h5g._path_valid
  File "h5py/_objects.pyx", line 54, in h5py._objects.with_phil.wrapper
  File "h5py/_objects.pyx", line 55, in h5py._objects.with_phil.wrapper
  File "h5py/h5l.pyx", line 212, in h5py.h5l.LinkProxy.exists
RuntimeError: Unable to get link info (message type not found)

Solved by reading the parent site collection. Also, some cleanup.