HAS_HDF5 only set when using HDF5_hdf5_LIBRARY_RELEASE in Release build

[Sa Wu]

In my latest dolfin build I noticed that even though ldd showed dolfin being linked against hdf5, dolfin.has_hdf5() yielded False. The new pybind11 interface needs HAS_HDF5 to be properly set in DolfinTargets.cmake for the python bindings for the TimeSeries, HDF5File, and proper configuartion of XDMFFile with hdf5 support. Trying around with the cmake HDF5 options it appears that HAS_HDF5 is only set and exported to DolfinTargets.cmake if, and only if, HDF5_hdf5_LIBRARY_RELEASE is set (building Release). The variables for paths to the cmake configuration of hdf5, to h5diff, or even the other variable for hdf5.so and hdf5_hl.so don't seem to affect HAS_HDF5 in any way.