Adjustments for "users shouldn't be able to change their username"

A few adjustments for rails 4 and in the tests.

refs #452
Setup default site for tests, don't rely on setup_config.yml

setup_config.yml is not on git and can be easily changed by anyone, possibly
breaking the tests. Now we have a method that sets up the site as expected
by the test suite.
Use serialize for ShibToken#data