build: add CentOS 8 support; drop CentOS 7

Refs: #5040, #5087
Change-Id: I6dcc5e9ee6b4839a6b3f15f1ad6dabf140301ae4
diff --git a/.jenkins.d/01-ndn-cxx.sh b/.jenkins.d/01-ndn-cxx.sh
index f10956c..6f50dba 100755
--- a/.jenkins.d/01-ndn-cxx.sh
+++ b/.jenkins.d/01-ndn-cxx.sh
@@ -1,10 +1,5 @@
 #!/usr/bin/env bash
-set -e
-
-JDIR=$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )
-source "$JDIR"/util.sh
-
-set -x
+set -ex
 
 sudo rm -f /usr/local/bin/ndnsec*
 sudo rm -fr /usr/local/include/ndn-cxx