ci: Always skip tasks tagged "install"

Software should never be installed or updated by the continuous
enforcement jobs.  This can cause unexpected outages or other problems
if applications or libraries unexpectedly.  Everything should already be
installed and in production before continuous enforcement begins, so
skipping install steps should not matter.

Most tasks that install software are tagged with the `install` tag.
When Jenkins runs `ansible-playbook` to apply configuration policy, it
will now skip any task that includes this tag.

vars/applyConfigPolicy.groovy

@@ -72,7 +72,8 @@ def generateStages(stages) {
                     playbook: playbook,
                     become: true,
                     vaultCredentialsId: 'ansible-vault',
-                    extras: '--diff'
+                    extras: '--diff',
+                    skippedTags: 'install'
             }
         }
     }