nightwatch e2e tests should be idempotent

[Jane Sandberg]

Jargon translation: idempotent = you get the same result no matter how many times you run a process.

Desired behavior: you can run the nightwatch test suite many times in a row, and get the same results each time.

Actual behavior: it passes the first time, but then it fails on subsequent runs until you reload the database with the eg_db_config script. There is a note about this in Open-ILS/src/eg2/CHEAT_SHEET.adoc, but it would be much nicer if you didn't have to worry about it.