Bump Guava 23.6 → 25.1 and add default feature

Bump Guava 23.6 → 25.1 and add default feature

This replaces the odl-guava-23 feature with odl-guava-25 and adds a
default odl-guava feature which downstreams should depend on.

Release notes:
* https://github.com/google/guava/releases/tag/v24.0
* https://github.com/google/guava/releases/tag/v24.1
* https://github.com/google/guava/releases/tag/v25.0
* https://github.com/google/guava/releases/tag/v25.1

Change-Id: Ied2e93b4d6546df5ecd521672a6945cbb59e4b8a
Signed-off-by: Stephen Kitt <skitt@redhat.com>