catch unicode encoding errors in json outputter

[gtmanfred]

What does this PR do?

Catch errors when unable to encode text to utf8 for the json outputter.

Tests written?

YES!!!

[rallytime]

Yay tests!!!

[damon-atkins]

Hi @rallytime and @gtmanfred
In develop, it's expected to be able to output Unicode. So testing Unicode fails seems the wrong approach.

C:\salt>salt-call -l info  pkg.list_pkgs  --out=json
{
    "local": {
        "LakeCity\u2122": "4.0.96.5684",
        "Indeo\u00ae Software": "(value not set)",
        "Skype\u2122 7.0": "7.0.102",
    }
}

This is not linked to an issue, so I can not see the source of the problem.
If the source needs to deal with Unicode it should have "from future import unicode_literals". In fact saltstack should just add the line to every file and release a beta.