[master] Add a minimal SSH test.pkg_opts minion cache.

[Rudd-O]

This only attempts to accelerate repeated contacts with the SSH minion. The amount of data formerly cached is not contemplated in this patch, due to the complexity of ensuring that all that data is invalidated.

What does this PR do?

Accelerates repeated contacts with SSH minions by roughly 1 second, or more if latency is high.

Halves the total amount of SSH connections established with SSH minions.

In particular, orchestration runs become faster.

Most of the change is indentation whitespace.

What issues does this PR fix or reference?

None.

Previous Behavior

Every SSH minion run was prefaced with a test.opts_pkg call, slowing down minion runs.

New Behavior

SSH minion runs recently contacted to obtain the test.opts_pkg
data are not contacted for that data anymore. Instead, this data is read from a local minion
cache file, which is properly locked to protect data integrity.

This is by default turned off.

Merge requirements satisfied?

[NOTICE] Bug fixes or features added to Salt require tests.

• Docs
• Changelog - https://docs.saltproject.io/en/master/topics/development/changelog.html
• No tests have been updated -- please point me in the right direction.

Commits signed with GPG?

Yes.

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[twangboy]

This will also need a test