Some more fixes for CI

* -v for nosetests to see easily test cases names
* increase timeout for NTP
* use `read_preference` instead of deprecated `slave_okay` in mongo/tokumx test suite [see this page](http://api.mongodb.org/python/current/api/pymongo/collection.html?highlight=read_preference#pymongo.collection.Collection.slave_okay) (we bundle pymongo==2.6.3)

Still some more work to do on 2 or 3 flaky tests.