views_coll_stats.js should use its own database

In SERVER-27421, the views tests were picked up by the parallel tester to be run in parallel. views_coll_stats.js uses the "views_stats" database, which is also used by views_stats.js. Unfortunately, both of these tests drop and recreate the database several times, which means that there's a chance they'll interfere with each other in a parallel test run.

views_coll_stats.js should just use its own unique database.