ci: Configure for release builds

.gitlab-ci.yml

@@ -5,7 +5,7 @@ stages:
 
 variables:
   DOCKER_IMAGE_BASE: registry.icinga.com/build-docker
-  ICINGA_BUILD_TYPE: snapshot
+  ICINGA_BUILD_TYPE: release
 
 .build: &build
   stage: build
@@ -42,7 +42,6 @@ variables:
     - icinga-build-upload-aptly
   only:
     - tags
-    - master
 
 build/centos/7:
   <<: *build