add tests for all blob schemas

[bhearsum]

While reviewing #145 I found an issue with one of the yml files it was changing. To my surprise, the tests still passed. It looks like this is because we don't have any tests for .validate() except for some apprelease blobs, and the whitelist blob. We should add tests for all the remaining blobs that use .validate().

(Imported from https://bugzilla.mozilla.org/show_bug.cgi?id=1310000)