(#1137) - Simply test and ensure setup clean db

So the problem with the previous test is that we had 2 tests using `PouchDB` constructor in a row which will not clean up the tests properly in between and cause intermittent failures, I have got a proper fix for this in https://github.com/daleharvey/pouchdb/pull/1158 but wanted to get rid of the intermittent first

The original test was more exhaustive, but very complicated, this test should be sufficient to make sure we dont regress