Refactor test suite for robustness

[chrisma]

In the entire test suite:

• When testing for the presence or absence of links or buttons, detect whether a page has an appropriate HTML tag with a given href attribute pointing to a named route, e.g. dashboard_path, rather than relying on brittle class names or link texts. Example: 458/450/RefactorVMPages #458 (comment)

• When visiting or checking for paths, use named routes instead of strings, e.g. new_request_path vs. vms/requests/new

• Rely on central test data storage in factories. If new versions of objects are needed, create a new factory and give it a descriptive name. If only attributes of objects are needed, use attributes_for() https://github.com/thoughtbot/factory_bot/blob/master/GETTING_STARTED.md#using-factories
  Example: e55e616