Support python3 and python2

[ericklaus-wf]

RIS's CI is broken because goverge does not work on python3, and RIS's underlying build container just started shipping python3 instead of python2. goverge doesn't work on python3 for several reasons:

• sub-module imports without "." prefix
• print statements (instead of print functions)

python2 supports sub-module imports. With future imports, it also supports print statements.

So this change should be compatible with both python2 and python3.

[aviary2-wf]

Security Insights

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Action Items

• Review PR for security impact; comment "security review required" if needed or unsure

• Verify aviary.yaml coverage of security relevant code

  Questions or Comments? Reach out on Slack: #support-infosec.

[ericklaus-wf]

I think there are still python3 related problems with this PR.