Migration from GCloud to Belgium

[bosa-cihan]

We should update our reference to the GCloud domain after the migration of REST Guideline to the Belgium Domain which has been planned for the end of April.

[pvdbosch]

FYI, belgif/rest-guide#91 is the issue for migration of the REST guide to https://belgif.be.

There are some changes in the maven build of the guide as well, they can be copied to the security guide. But that can wait until the REST guide is migrated and these changes are fully validated.

I'll notify you when the REST guide migration is finished.