Update so parent pom in cnf-adapter

Update so parent pom in cnf-adapter

- update so parent pom (1.12.1-SNAPSHOT -> 1.15.0-SNAPSHOT)
- this may seem like a huge jump, but this is actually not
  changing much:
  - update snakeyaml (1.26 -> 1.31)
  - change scope of some test deps from compile to test (mockito, junit-toolbox)
- keep the h2 test dependency at the 1.X version since updating
  it would require a flyway update.
  I don't want to do that here to reduce the risk of breaking
  changes

Issue-ID: SO-4180
Change-Id: I7685390183736dab50a53f8cbd9565f70e0f72d5
Signed-off-by: Fiete Ostkamp <Fiete.Ostkamp@telekom.de>