mysql update docs with env vars, update test with json field, fill cl…

[kristijorgji]

• drop the test db after test finishes. I runned the tests several times and had many random named databases created, this fixes it
• update docs to specify the mysql env vars used in order to make it easier for contributing
• add one json field type in the example update models and test for that too

[kyleconroy]

The ondeck example is shared across MySQL and PostgreSQL, so I'd like to keep it the same. Please remove the added JSON column. A MySQL JSON example already exists in the form of an end-to-end test.

Really appreciate the README updates!

[kristijorgji]

The ondeck example is shared across MySQL and PostgreSQL, so I'd like to keep it the same. Please remove the added JSON column. A MySQL JSON example already exists in the form of an end-to-end test.

Really appreciate the README updates!

Done, reverted that change please re-review

[kyleconroy]

Thanks! I've rebased your changes onto master and will merge once the build passes.