Add validation to put_events

[gruebel]

Fixes #3384

It is a quite interesting behaviour of the put_events endpoint, because each event is validated separately and the status is send back for all of them.

[coveralls]

Coverage increased (+0.01%) to 94.574% when pulling 347fb43 on gruebel:add-put-events-validation into a31599d on spulec:master.

[bblommers]

Hey @gruebel, would you mind splitting up the test scenarios in multiple methods?
Would be good to also test a scenario with multiple events, some valid, some invalid.

[gruebel]

I also removed the weird test_rule_tagging_sad test and added the correct way of testing them.

[bblommers]

Looks like it's failing in Py2:
AttributeError: 'module' object has no attribute 'JSONDecodeError'

[gruebel]

@bblommers is there actually a plan to drop Python 2 support at some point?

[bblommers]

There's no plan yet, @gruebel. There's still a significant portion of people that are stuck with Py2, and we want to keep Moto available to them as long as possible.
Thanks for the PR!