Align haproxy logging config with charm-helpers

The previous config didn't actually log anything, and it has been fixed
for classic OpenStack API charms through charm-helpers. We need to
update layer-openstack as well to reflect those changes to reactive
OpenStack API charms.

Closes-Bug: #1697002
Related-Bug: #1940037
Change-Id: I523369673471f63346428f7f739a2429aa5084b3

templates/haproxy.cfg

@@ -1,10 +1,24 @@
 global
-    log {{ options.local_host }} local0
-    log {{ options.local_host }} local1 notice
+    # NOTE: on startup haproxy chroot's to /var/lib/haproxy.
+    #
+    # Unfortunately the program will open some files prior to the call to
+    # chroot never to reopen them, and some after. So looking at the on-disk
+    # layout of haproxy resources you will find some resources relative to /
+    # such as the admin socket, and some relative to /var/lib/haproxy such as
+    # the log socket.
+    #
+    # The logging socket is (re-)opened after the chroot and must be relative
+    # to /var/lib/haproxy.
+    log /dev/log local0
+    log /dev/log local1 notice
     maxconn 20000
     user haproxy
     group haproxy
     spread-checks 0
+    # The admin socket is opened prior to the chroot never to be reopened, so
+    # it lives outside the chroot directory in the filesystem.
+    stats socket /var/run/haproxy/admin.sock mode 600 level admin
+    stats timeout 2m
 
 defaults
     log global