e2e: minimize Consul ACL policies used in e2e tests

Issue #7523 documents the Consul ACLs used in each Consul interface
used by Nomad. Minimize the policies used in e2e tests so that we
are setting a good example.

e2e/consulacls/nomad-client-policy.hcl

@@ -4,10 +4,10 @@ service_prefix "" {
   policy = "write"
 }
 
-node_prefix "" {
-  policy = "write"
-}
-
 agent_prefix "" {
   policy = "read"
 }
+
+node_prefix "" {
+  policy = "read"
+}

e2e/consulacls/nomad-server-policy.hcl

@@ -7,10 +7,10 @@ service_prefix "" {
   policy = "write"
 }
 
-node_prefix "" {
-  policy = "write"
-}
-
 agent_prefix "" {
   policy = "read"
 }
+
+node_prefix "" {
+  policy = "read"
+}