community/py3-{dask,distributed}: upgrade to 2021.1.0

To get py3-distributed running again, some packages are needed from testing/ so I moved them over.

• @dsabogal I'm moving over hwloc and openmpi, is that alright with you?
• @fab I'm moving over py3-arrow, is that alright with you? Also please package py3-chai so tests can be enabled
• @Leo I'm moving over py3-pkgconfig, is that alright with you?

James White maintains py3-h5py but the package was both outdated and disabled, so I'm guessing he isn't around anymore.