Tests for HDF5Writer engine are missing native HDF5 read validation

Created by: chuckatkins

Three of the test in testing/adios2/engine/hdf5/TestHDF5WriteRead.cpp write data using the HDF5Writer engine and validate it using HDF5 natively:

• ADIOS2HDF5WriteHDF5Read1D8
• ADIOS2HDF5WriteHDF5Read2D2x4
• ADIOS2HDF5WriteHDF5Read2D4x2

The native HDF5 read validation still needs to be implemented. See testing/adios2/engine/adios1/TestADIOS1WriteRead.cpp for an example of how the ADIOS1Writer engine is used with ADIOS1 natively reading back the data to validate. Once implemented, you should be able to run the tests via ./bin/TestHDF5WriteRead and have it pass.