Merge branch 'feature/update-test-environments' into 'master'

Update test environments

- No longer test with clang 3.5.
- Add clang 3.8 from Debian 8 + backports
- Add gcc 5.4 + clang 3.8 from Ubuntu 16.04 LTS.
- Use `duneci-standard-test`

See merge request !146

.gitlab-ci.yml

 ---
 debian:9--gcc:
   image: duneci/base:9
-  script:
-  - ./bin/dunecontrol --current --opts=/duneci/opts.gcc all
-  - ./bin/dunecontrol --current make build_tests
-  - cd build-cmake; duneci-ctest
+  script: duneci-standard-test
 
 debian:9--clang:
   image: duneci/base:9
-  script:
-  - ./bin/dunecontrol --current --opts=/duneci/opts.clang all
-  - ./bin/dunecontrol --current make build_tests
-  - cd build-cmake; duneci-ctest
+  script: duneci-standard-test --opts=/duneci/opts.clang
 
 debian:8--gcc:
   image: duneci/base:8
-  script:
-  - ./bin/dunecontrol --current --opts=/duneci/opts.gcc all
-  - ./bin/dunecontrol --current make build_tests
-  - cd build-cmake; duneci-ctest
+  script: duneci-standard-test
 
-debian:8--clang:
-  image: duneci/base:8
-  script:
-  - ./bin/dunecontrol --current --opts=/duneci/opts.clang all
-  - ./bin/dunecontrol --current make build_tests
-  - cd build-cmake; duneci-ctest
+debian:8-backports--clang:
+  image: duneci/base:8-backports
+  script: duneci-standard-test --opts=/duneci/opts.clang
+
+ubuntu:16.04--gcc:
+  image: duneci/base:16.04
+  script: duneci-standard-test
+
+ubuntu:16.04--clang:
+  image: duneci/base:16.04
+  script: duneci-standard-test --opts=/duneci/opts.clang