Modified gitlab-ci to use Registry for docker images

.gitlab-ci.yml

 build-gfortran:
-  image: ubuntu:16.10
+  image: iffregistry.fz-juelich.de/fleur/fleur:latest
   stage: build
   cache: 
      paths:
        - build
   script:
-    - apt-get update -qq && apt-get install -y -qq build-essential gfortran gfortran-6 g++-6 gcc-6 binutils-gold git cmake libxml2-dev liblapack-dev libblas-dev doxygen libopenmpi-dev libscalapack-mpi-dev
     - cd /builds/fleur/fleur; ./configure.sh GITLAB; cd build; make 
 test-gfortran:
-  image: ubuntu:16.10
+  image: iffregistry.fz-juelich.de/fleur/fleur:latest
   stage: test
   cache:
      paths:
        - build
   script:
-    - apt-get update -qq && apt-get install -y -qq build-essential gfortran gfortran-6 g++-6 gcc-6 binutils-gold git cmake libxml2-dev liblapack-dev libblas-dev libopenmpi-dev libscalapack-mpi-dev
     - ulimit -s unlimited ;export juDFT_MPI="mpirun -n 2 --allow-run-as-root ";cd /builds/fleur/fleur/build;ctest
   artifacts:
      paths:
@@ -24,13 +22,12 @@ test-gfortran:
     
 
 pages:
-  image: ubuntu:16.10
+  image: iffregistry.fz-juelich.de/fleur/fleur:latest
   stage: deploy
   cache:
      paths:
        - build
   script:
-    - apt-get update -qq && apt-get install build-essential gfortran gfortran-6 g++-6 gcc-6 binutils-gold git cmake libxml2-dev liblapack-dev libblas-dev libopenmpi-dev libscalapack-mpi-dev doxygen
     - cd /builds/fleur/fleur/build ; make doc
     - mv docs/html/ ../public/
   artifacts: