HDF5 Build Fixes, master branch (2018.09.18.)

Fixed how the ZLIB library path would be passed to the HDF5 configuration. Since it turns out that the previous setup had no effect, and in "Athena mode" HDF5 still got compiled against /usr/lib/libzlib.so. (Unfortunately the nightly web logs don't show this, I only came across this behaviour while trying to cross compile AnalysisBaseExternals for ARM. It's a long story... 😛)

At the same time made sure that the CMAKE_BUILD_TYPE setting of the ATLAS project would be propagated to HDF5's build.

As it turns out this really only affects AthAnalysisExternals at the moment, none of the other "Athena based" projects build HDF5. Still, I wanted to fix this with some haste.

Tagging @kzoch as the developer of this package.