Unexpected result of koji_util.get_srpm_arches

[mizdebsk]

When build_arches parameter of koji_util.get_srpm_arches (or corresponding config variable) contains non-canonical arch, get_srpm_arches silently skips that arch.

Reproducer:

import koji
from koschei.backend import koji_util
ks = koji.ClientSession('https://koji.fedoraproject.org/kojihub')
tag_arches = koji_util.get_koji_arches(ks, 'f29-build')
koji_util.get_srpm_arches(ks, all_arches=tag_arches, build_arches=tag_arches, nvra='uboot-tools-2018.03-0.5.rc3.fc29.src')

Expected output:
{'aarch64', 'armv7hl', 'i686', 'ppc64', 'ppc64le', 's390x', 'x86_64'}
Actual output:
{'aarch64', 'ppc64', 'ppc64le', 's390x', 'x86_64'}

Proposed solution 1: make get_srpm_arches raise an exception if non-canonical arch is passed in build_arches
Alternative solution 2: make get_srpm_arches map build_arches to canonical arches

@msimacek Which solution is better in your opinion?

[msimacek]

I think either is fine. I'd personally prefer to canonicalize the arch (it seems easier)