Use standard `NETRC` environment variable name for netrc credential file

Dduvallrequested to merge
master-I0948e0c19106af04d23da5321899db994fa1a0c5 into master

The previously used environment variable name required the downstream
tool (release/make-release/automatic-branch-cut) to set HOME and
symlink the netrc file. If we instead use the standard NETRC
environment variable name, the file should be picked up by Python's
requests library and there will be no need for special handling in the
branch cut script.

Related MRs:

Edited by Dduvall

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