Changed viz tests to leave all visualizations. New dashboard tests.

[LeeDr]

Prior to this change, each visualization test started by loading an empty kibana index. Now that only happens in once for all visualize tests in the before method of /test/apps/visualize/index.js.
This saves the time to create the default index pattern each time so the whole test run is faster.
This also leaves the saved visualizations so they can be used in the dashboard tests.
Yes, I know that makes the dashboard tests dependent on the visualization tests. But I think there's some advantage to using visualizations that were created in this version vs. loading a previously saved kibana index with saved visualizations (that could be an upgrade test).

Still TODO: Check Save Time checkbox on saving dashboard and then verify it.

[LeeDr]

@acs FYI, this isn't quite ready for review yet, but there are passing dashboard tests that add multiple visualizations, save the dashboard, get the titles of all the panels, check the location attributes, etc.
You could look through them, try running them, ask questions here, etc.
I started working on a resize method for a visualization on a dashboard but haven't gotten that working yet.