Hotfix tweaks

[kflynn]

Best reviewed commit-by-commit. This is all cleanup of details for the 1.x hotfix process (and, soon, the 2.x
hotfix process too).

• Clean up indentation.
• Consistent ;\
• Fix missing `
• Use $$( ) instead of `` (it's slightly easier to catch a missing close-paren than a missing backtick).
• Missing semicolon
• Drop excess ;
• Allow overriding the hotfix commitish using HOTFIX_COMMIT. Fix a couple of other small things (e.g. an excess \ in the regex).
• Fix push tag.
• Fix AWS secret key assignment.