intermediate-registry: handle socat warning out

Zuul switched to a new base image, and it seems the new socat puts out
a warning (something like

 ...  socat[489590] W ioctl(5, IOCTL_VM_SOCKETS_GET_LOCAL_CID, ...): Inappropriate ioctl for device

for reference).

Grep the output so we only get the line about what port it is
listening on.

Change-Id: I74fb86a9158b45e6601ee1fbc199ba80cd4991fe

roles/pull-from-intermediate-registry/tasks/main.yaml

@@ -9,7 +9,11 @@
 # fact that docker does not correctly parse ipv6 addresses.  The socat
 # process will terminate when the playbook ends.
 - name: Start socat to work around https://github.com/moby/moby/issues/39033
-  shell: "socat -d -d TCP-LISTEN:0,fork TCP:{{ buildset_registry.host | ipwrap }}:{{ buildset_registry.port }} 2> {{ zuul.executor.work_root }}/socat_port &"
+  shell: |
+    set -o pipefail
+    socat -d -d TCP-LISTEN:0,fork TCP:{{ buildset_registry.host | ipwrap }}:{{ buildset_registry.port }} 2>&1 | grep --line-buffered 'listening on' >  {{ zuul.executor.work_root }}/socat_port &
+  args:
+    executable: /bin/bash
 
 # Use slurp instead of file lookup to make this testable on a fake
 # executor node.

roles/push-to-intermediate-registry/tasks/push.yaml

@@ -9,7 +9,11 @@
 # fact that docker does not correctly parse ipv6 addresses.  The socat
 # process will terminate when the playbook ends.
 - name: Start socat to work around https://github.com/moby/moby/issues/39033
-  shell: "socat -d -d TCP-LISTEN:0,fork TCP:{{ buildset_registry.host | ipwrap }}:{{ buildset_registry.port }} 2> {{ zuul.executor.work_root }}/socat_port &"
+  shell: |
+    set -o pipefail
+    socat -d -d TCP-LISTEN:0,fork TCP:{{ buildset_registry.host | ipwrap }}:{{ buildset_registry.port }} 2>&1 | grep --line-buffered 'listening on' >  {{ zuul.executor.work_root }}/socat_port &
+  args:
+    executable: /bin/bash
 
 # Use slurp instead of file lookup to make this testable on a fake
 # executor node.