Update dx run --clone helpstring to include analysis IDs
Configure pep8 as a linter in arcanist
Only run pep8 on Python files
PTFM-11771 Allow dx set_details -f to supply JSON from a file.

Summary: Also added unit tests, including unit tests for existing functionality.

Test Plan: Unit tests for "dx set_details".

Reviewers: psung

Reviewed By: psung

Subscribers: klai

Differential Revision: https://phabricator.dnanexus.com/D113
Changelog and version updates for v0.120.0