concat instead of redirect so we merge skips

cerncentostests.sh

@@ -6,16 +6,8 @@ yum install git -y
 git clone https://gitlab.cern.ch/linuxsupport/cern_centos_functional_tests.git
 cd cern_centos_functional_tests;
 
-# Disable certain tests for docker base image
-cat > ./skipped-tests.list  <<DELIM
-# This file contains list of tests we need/want to skip
-# Reason is when there is upstream bug that we're aware of
-# So this file should contain:
-#  - centos version (using $centos_ver)
-#  - test to skip (tests/p_${name}/test.sh)
-#  - reason why it's actually skipped (url to upstream BZ, or bug report)
-# Separated by |
-7|tests/0_common/00_centos_repos.sh|We want to keep CERN repos enabled
+# Disable certain tests for docker base image, concat with defaults
+cat >> ./skipped-tests.list  <<DELIM
 7|tests/cern_specific/3_check_cern_ntp.sh|No NTP on base image
 DELIM