FindHDF5: does not find zlib and libdl with HDF5_ROOT since rework in 3.6
I don't know whether this was intended, but since the rework of the FindHDF5 with 3.6 external libraries like the zlib or libdl are not found or included anymore. The variables HDF5_z_LIBRARY_(RELEASE/DEBUG) and HDF5_dl_LIBRARY_(RELEASE/DEBUG) are no longer set. Depending on the HDF5 compile options other libraries may be affected as well. The only libs that are found are the hdf5 and hdf5_{__lang} libs, as FindHDF5 only searches for these.
Tested on Ubuntu 16.04 with self-compiled HDF5 1.10-patch1 using the automake configure script and HDF5_ROOT set to correct folder.