Don't offline signing node

Do not offline the signing node. Right now we only run tag-releases on
that node.

Add also a note to our REVIEWING list about these long-lived nodes.

Change-Id: I7ddea40069add66dc07ee754092c8c236c62b53c

REVIEWING.rst

@@ -77,3 +77,12 @@ Removing check-requirements job
   the reviewer should verify that the project has been removed from
   projects.txt already or that this project-config change depends
   on the review to remove it.
+
+Jobs for persistent node
+========================
+
+In general, nodes are off-lined after a job run. Some special nodes
+are not off-lined and long-lived. Ensure for these nodes that any job
+running on them is handled in zuul/openstack_functions.py.
+
+Current nodes that are long-lived are: proposal, release, signing, wheel-mirror-*

zuul/openstack_functions.py

@@ -52,11 +52,13 @@ def set_node_options(item, job, params):
     hook_re = r'^hook-(.*?)-(rtfd)$'
     wheel_re = r'^wheel-(build|release)-.*$'
     reprepro_re = r'^reprepro-(import|release)-.*$'
+    signing_re = r'^tag-releases$'
     # jobs run on the persistent proposal, release, and wheel build
     # workers
     if (re.match(proposal_re, job.name) or
         re.match(release_re, job.name) or
         re.match(hook_re, job.name) or
         re.match(reprepro_re, job.name) or
+        re.match(signing_re, job.name) or
         re.match(wheel_re, job.name)):
         reusable_node(item, job, params)