sapling: disable flaky tests on github getdeps cli

[ahornby]

Summary: X-link: https://github.com/facebookincubator/zstrong/pull/1017

• disable flaky tests as per comment in Makefile
• fix Makefiles JOBS sed expression to be macOS make compatible
• remove Makefile comment in multiline shell, macOS make didn't like it
• remove hexdump from deps for macOS where it is a system util

Reviewed By: quark-zju

Differential Revision: D64781284

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D64781284

[facebook-github-bot]

This pull request has been merged in facebook/sapling@0788e00b12be48174b3e9a428cc2201f2f40d624.