Make the buildset registry port configurable

This will allow us to run the role twice on the same host.  This
will be useful when we test changes to this role.

Change-Id: I97baeb3172298648bcfef26c5be635ad4be036f0

roles/run-buildset-registry/README.rst

@@ -11,6 +11,11 @@ single change can share the registry.
 
    Path for the registry volumes.
 
+.. zuul:rolevar:: buildset_registry_port
+   :default: 5000
+
+   The port on which the registry should listen.
+
 **Return Values**
 
 .. zuul:rolevar:: buildset_registry

roles/run-buildset-registry/defaults/main.yaml

@@ -1 +1,2 @@
 buildset_registry_root: "{{ ansible_user_dir }}/buildset_registry"
+buildset_registry_port: 5000

roles/run-buildset-registry/tasks/main.yaml

@@ -47,7 +47,7 @@
     state: started
     restart_policy: always
     ports:
-     - "5000:5000"
+     - "{{ buildset_registry_port }}:5000"
     volumes:
       - "{{ buildset_registry_root }}/tls:/tls"
       - "{{ buildset_registry_root }}/conf:/conf"
@@ -55,7 +55,7 @@
   set_fact:
     buildset_registry:
       host: "{{ ansible_host }}"
-      port: 5000
+      port: "{{ buildset_registry_port }}"
       username: zuul
       password: "{{ registry_password }}"
       cert: "{{ certificate }}"