route-proxy: a bus account, to read its membership

The proxy reads its routes and the mesh's addresses from its membership
on the bus rather than from a file alone (novox/hq ADR 0167, issue 191).

modules/route-proxy/module.json

@@ -25,6 +25,9 @@
     "acme-ca": "${dir:state}/acme-ca.json",
     "internal-acme-ca": "${dir:state}/internal-acme-ca.json"
   },
+  "own-secrets": {
+    "broker": "${dir:mesh-state}/broker"
+  },
   "listens": [
     {
       "name": "http",
@@ -48,6 +51,12 @@
       "mode": "0700",
       "place": "."
     },
+    {
+      "id": "mesh-state",
+      "type": "directory",
+      "mode": "0700",
+      "place": "mesh"
+    },
     {
       "id": "routes-dir",
       "type": "directory",
@@ -137,7 +146,8 @@
       "volumes": [
         "${dir:routes-dir}:/routes:ro",
         "${dir:acme-cache}:/acme",
-        "${dir:ca-dir}:/ca:ro"
+        "${dir:ca-dir}:/ca:ro",
+        "${dir:mesh-state}/broker:/run/secrets/broker:ro"
       ],
       "env": {
         "ROUTES": "/routes/mesh.json",
@@ -145,7 +155,8 @@
         "TLS_LISTEN": ":443",
         "ACME_CACHE": "/acme",
         "ACME_CA_BUNDLE": "/ca/root.crt",
-        "INTERNAL_ACME_CA_BUNDLE": "/ca/internal-root.crt"
+        "INTERNAL_ACME_CA_BUNDLE": "/ca/internal-root.crt",
+        "MESH_BROKER_FILE": "/run/secrets/broker"
       },
       "restart-on": [
         "trust",