build: add CentOS 8 support; drop CentOS 7

Refs: #5040, #5087
Change-Id: I6dcc5e9ee6b4839a6b3f15f1ad6dabf140301ae4
diff --git a/.jenkins b/.jenkins
index 934aceb..b368a74 100755
--- a/.jenkins
+++ b/.jenkins
@@ -1,5 +1,8 @@
 #!/usr/bin/env bash
 set -e
+source .jenkins.d/util.sh
+
+export WAF_JOBS=${WAF_JOBS:-1}
 
 nanos() {
     # Cannot use date(1) because macOS does not support %N format specifier