Initially done via --auto-correct, then manually linted the resulting
code (that would otherwise introduce a bunch of offenses).

Changes generated with:

`rubocop --only Style/SymbolProc --auto-correct`

Changes generated with:

`rubocop --only Style/RedundantReturn --auto-correct`

Changes generated with:

`rubocop --only Style/RaiseArgs --auto-correct`

Fixup against bce649bd.

Changes generated with:

`rubocop --only Style/SpecialGlobalVars --auto-correct`

Changes generated with:

`rubocop --only Style/TrailingCommaInArrayLiteral --auto-correct`

Changes generated with:

`rubocop --only Layout/EmptyLinesAroundModuleBody --auto-correct`

IO#close() seems entirely wrong here, and very likely is the cause for
our defunct subprocesses; I thought IO#close() did an implicit
Process.wait(), but it seems to actually just flush buffers and
forcefully close immediately, even if the process has not exited yet.

If this commit fixes our issues I'll do a pass through our other uses
of IO#close() for subprocesses and fix them too.

Will-fix: #17551

If these methods are called from within a try_for() block and the
timeout occurs when running the IO.popen() call, but before the
p.close(), then we get a lingering defunct process. So let's ensure
the processes are cleaned up even in that case.

Will-fix: #17551

It's easier to debug/test this way.

This will be useful for a image bumping mode I'm about to add where
the user is shown what a candidate image matches on the screen, so the
user can verify that it's correct.

I am about to implement a feature where the last match can be used to
"bump" the image after allowing more fuzziness.

Basically it is a wrapper around OpenCV's matchTemplate() which can be
used for image matching, just like Sikuli's find() etc. Since Ruby
doesn't have any (working) OpenCV bindings we resort to calling a
Python script.

Currently it's not used, but stay tuned!

Refs: #15460