Make Cold Storage Service tests run

The following test class

• https://github.com/nuxeo/nuxeo-coldstorage/blob/v2021.0.0-rc.20/nuxeo-coldstorage/src/test/java/org/nuxeo/coldstorage/service/DummyTestColdStorage.java
• https://github.com/nuxeo/nuxeo-coldstorage/blob/v2021.0.0-rc.20/nuxeo-coldstorage/src/test/java/org/nuxeo/coldstorage/service/S3TestColdStorage.java

are just not run because the class name does not match the pattern :

          <includes>
            <include>**/Test*.java</include>
            <include>**/*Test.java</include>
          </includes>

defined in parent pom 's surefire plugin config https://github.com/nuxeo/nuxeo-lts/blob/2021/pom.xml#L4996

Typically, the CI does not give any status:

• https://jenkins.napps.dev.nuxeo.com/job/nuxeo/job/nuxeo-coldstorage/job/lts-2021/44/testReport/
  meaning we don't even know of those tests pass :|

We must rename these classes.