MWA Beam path is not portable

[d3v-null]

The MWA beam path is hardcoded here:

sivio/sivio/beam.py

Line 146 in cd4100f

"/home/kariuki/mwa_pb/mwa_full_embedded_element_pattern.h5"

it would be more portable to grab this from the MWA_BEAM_FILE environment variable like this:

hbeam = mwa_hyperbeam.FEEBeam(os.environ['MWA_BEAM_FILE'])

[d3v-null]

actually, providing no argument works too:

https://github.com/MWATelescope/mwa_hyperbeam/blob/8f72721f01b8950a8ac3400fd73cdc00a7482eca/examples/fee.py#L14-L17