Make neo4j-graphql#252 less painful, mark not-isolated tests

With this commit you can run

```
npm run test-isolated
```

over and over again and the tests should pass. This does not fix the
issue mentioned above but it makes it less painful. At least I can make
my changes and run all tests exluding those that are not isolated. When I'm done
with my changes I can re-import the data and run all the tests, even those that
are not isolated.

This is what I did to get all the tests passing on my machine:

```
sudo rm /var/lib/neo4j/data/databases/* -r
sudo cp -rp ~/Downloads/temp/neo4j-graphql-js/recommendations.db/ /var/lib/neo4j/data/databases/graph.db
sudo systemctl restart neo4j.service
```

Very annoying.

@johnymontana @michaeldgraham do you know if there is a single command
that brings the database into a state where it was *before* running the
test case? Something that we could use in a `beforeEach` or `afterEach`?

See: neo4j-graphql#252 (comment)

package.json

@@ -17,7 +17,8 @@
     "parse-tck": "babel-node test/helpers/tck/parseTck.js",
     "test-tck": "nyc ava --fail-fast test/tck/",
     "report-coverage": "nyc report --reporter=text-lcov > coverage.lcov && codecov",
-    "test-all": "nyc ava test/*.js --verbose",
+    "test-all": "nyc ava test/ --verbose",
+    "test-isolated": "nyc ava test/ --verbose --match='!*not-isolated*'",
     "debug": "nodemon ./example/apollo-server/movies.js --exec babel-node --inspect-brk=9229 --nolazy",
     "debug-typedefs": "nodemon ./example/apollo-server/movies-typedefs.js --exec babel-node --inspect-brk=9229 --nolazy"
   },