Fix and enforce javadoc issues

[ctron]

Currently the build is full or warnings like this:

[WARNING] * @throws KapuaException
[WARNING] ^
[WARNING] /home/travis/build/ctron/kapua/service/security/authorization/api/src/main/java/org/eclipse/kapua/service/authorization/role/RolePermissionService.java:98: warning: no description for @throws
[WARNING] * @throws KapuaException
[WARNING] ^
[WARNING] /home/travis/build/ctron/kapua/service/security/authorization/api/src/main/java/org/eclipse/kapua/service/authorization/role/RolePermissionXmlRegistry.java:27: warning: no description for @return
[WARNING] * @return
[WARNING] ^
[WARNING] /home/travis/build/ctron/kapua/service/security/authorization/api/src/main/java/org/eclipse/kapua/service/authorization/role/RolePermissionXmlRegistry.java:36: warning: no description for @return
[WARNING] * @return
[WARNING] ^
[WARNING] /home/travis/build/ctron/kapua/service/security/authorization/api/src/main/java/org/eclipse/kapua/service/authorization/role/RolePermissionXmlRegistry.java:45: warning: no description for @return
[WARNING] * @return

I would suggest to 1) fix existing issues by dropping empty javadoc fragments and find a way to enforce that no empty javadoc fragments get added in the future.

If we have actual javadoc that is fine, but empty javadoc snippets and warnings in the build should be fixed IMHO.

[ctron]

This would also fix issues with Travis and "too long" console output

[Coduz]

We are slowly add javadoc as we add new stuff and fix bugs.
So we move this issue on to the next release.