jobs/bump-lockfile: limit to single run at a time

Right now when the bump-lockfiles job runs it kicks off two runs of
bump-lockfile (one for each stream) at the exact same time. This might
be what is causing our timeouts to be getting hit lately (primarily
because the ppc64le runs are taking longer) [1].

Let's limit the bump-lockfile job to a singular run at any given time.

[1] coreos/fedora-coreos-tracker#1579

Author: dustymabe

jobs/bump-lockfile.Jenkinsfile

@@ -62,7 +62,7 @@ def getLockfileInfo(lockfile) {
 def cosa_memory_request_mb = 10.5 * 1024 as Integer
 def ncpus = ((cosa_memory_request_mb - 512) / 1536) as Integer
 
-lock(resource: "bump-${params.STREAM}") {
+lock(resource: "bump-lockfile") {
     cosaPod(image: cosa_img,
             cpu: "${ncpus}", memory: "${cosa_memory_request_mb}Mi",
             serviceAccount: "jenkins") {