testing 5.7 and JSON

[shlomi-noach]

This PR runs localtests on 5.7. It also adds JSON datatype tests.

[arthurnn]

How do we run the localtests?
Just run the test.sh script?
Also, do they run on ci?

[shlomi-noach]

So localtests are not yet running from CI, unfortunately, and there's a measure of a manual setup to make them work.

See #427 for a contributor's work to make that run on CI. I think, however, that work on this has stopped seeing that the PR is stale. Also see discussion on #425

TL;DR you need a local master/replica setup, with your own implementation for gh-ost-test-mysql-master and gh-ost-test-mysql-replica.

Another consideration is that, at least up till now, I ran these tests on 5.6. We might want to run all tests on 5.6 AND 5.7 AND whatever else.

[arthurnn]

I will take a look.

On LHM, we had a few scripts to setup the master-replica for tests https://github.com/soundcloud/lhm/blob/master/bin/lhm-spec-setup-cluster.sh , but we also didn't run that on CI

[shlomi-noach]

Hmm messed this branch up ; continued elsewhere.