document log levels and warn on all logging below info

[jfindlay]

What does this PR do?

Document log levels and warn about sensitive data on all logging below info

I also wanted to warn on insecure levels of log_level_logfile, but this is not possible at present because of the following complications:

Running a check in salt.utils.verify.verify_log against log_level_logfile results in that config being set to None because that is what it is in salt.config.

salt.minion and salt.utils.cloud both set log_level_logfile to info as advertised by the logging docs and the minion config docs, but these are all incorrect and preempted by salt.utils.parsers, which sets log_level_logfile indiscriminately to warning. I have also verified this with a 2016.3.2 install.

If advised, I will submit another pull request against develop unifying these contradictory defaults to warning or info and update the release notes. I think warning would be better since that is what effectively happens and we should change salt.minion and salt.utils.cloud and the docs to that.

In my opinion, salt.config should be considered the authority on option defaults so that, for example, salt.utils.parsers can source its defaults from there rather than provide duplicate or contradictory defaults. What do you think, @s0undt3ch?

What issues does this PR fix or reference?

none

Tests written?

Yes

[s0undt3ch]

Agreed, let's unify.