cta: revert back to scientificlinux

cta-build.yml

@@ -13,7 +13,7 @@ before_script:
 cta_srpm:
   stage: build:srpm
   retry: 1
-  image: centos:7
+  image: scientificlinux/sl:7
   script:
     - yum install -y gcc-c++ cmake make rpm-build
     - mkdir build_srpm
@@ -32,7 +32,7 @@ cta_rpm:
     - tags
   stage: build:rpm
   retry: 1
-  image: centos:7
+  image: scientificlinux/sl:7
   script:
     - yum-config-manager --add-repo=https://storage-ci.web.cern.ch/storage-ci/eos/citrine-depend/el-7/x86_64/
     - rpm -import https://storage-ci.web.cern.ch/storage-ci/storageci.key