setup.py: RPath Issue on OSX with ADIOS1?

[ax3l]

@ChristopherMayes observed an rpath issue with setu.py based installs from PyPI with 0.7.1a regarding RPaths of our ADIOS1 wrapper library.

In 0.8.0 we will only build this when ADIOS1 is actually used, but the problem could still be there (when ADIOS1 is present):

>>> import openpmd_api
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: dlopen(/opt/local/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/openpmd_api.cpython-36m-darwin.so, 2): Library not loaded: @rpath/libopenPMD.ADIOS1.Serial.dylib
  Referenced from: /opt/local/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/openpmd_api.cpython-36m-darwin.so
  Reason: image not found

Environment

HDF5: 1.10.4
h5py: 2.9.0
macOS Mojave (latest)
python 3.6.8