Fix integration tests to run with Spring Boot 2.6.1

This bundles Jetty >9.4.44 which disables using "u0000" ("NUL")
character from being used in the path of Spring Boot applications.
Also, this bundles a Jackson version that refuses to encode unencoded
XML characters on-the-fly.
Also fix run order of tests.

Fixing tests so we can release S3Mock.

Fixes #320