Improve build config, work around issues.

[prabhuramachandran]

• Work around PyOpenCL issue for now: https://github.com/inducer/pyopencl/issues/535
• Add a cron schedule to run the tests so we catch errors due to changes in upstream packages early.
• Always test with latest cyarray and compyle.
• Improve requirements, we don't need meshio as it is optional but should test with h5py.
• The requirements.txt does not need to run off master cyarray and compyle anymore.