Test/nagios test signup

they have response.json as a dict instead of response.json()

now the webapp_login test looks nice and clean. soledad next.

nagios_test.run takes a function and executes it.
If it returns nothing or 0 and OK nagios message is printed.
If it returns sth. else this will be printed a a warning
If it raises an exception that will result in a CRITICAL report.

This way we can keep the nagios things outside the test cases and just write simple functions that either return 0, a warnign or raise a meaningful exception