pyuvdata/tests/test_uvdata.py: fix test_select_bls()
pyuvdata/tests/test_uvdata.py: fix test_select_bls()

`sorted((1, 2, 'string'))` no longer works in Python 3, and there was a zip()
call that needed to be wrapped in a list().

HERA-Team/pyuvdata,HERA-Team/pyuvdata,HERA-Team/pyuvdata,HERA-Team/pyuvdata