Fix test for duplicate service name

There is a uniqueness constraint on service `name` and `email_from`.

When you try to insert a row which has _both_ constraints, there is no
guarantee which one the operation will fail on.

This means that, when handling the exception, service `name` is not
reliably available, because sometimes the operation fails on the
`email_from` constraint instead.

This caused the tests to fail non-deterministically because they were
looking for the service `name` in the error message. As a fix, this
commit does two things:

1. Return either the service `name` or `email_from` in the error
   message, depending which is available.

2. Modify the test to pass on _either_ of the two possible error
   messages.

This is not ideal, but I can’t think of a way to maintain the original
behaviour, and have reliably passing tests.

app/errors.py

@@ -64,6 +64,8 @@ def register_errors(blueprint):
                 'duplicate key value violates unique constraint "services_email_from_key"' in e.orig.pgerror):
             return jsonify(
                 result='error',
-                message={'name': ["Duplicate service name '{}'".format(e.params.get('name', ''))]}
+                message={'name': ["Duplicate service name '{}'".format(
+                    e.params.get('name', e.params.get('email_from', ''))
+                )]}
             ), 400
         return jsonify(result='error', message="Internal server error"), 500