Add EndpointMapOverride parameter

This allows overriding the calculated EndpointMap, which is useful
in some cases such as deploying compute-only stacks which reference
some existing endpoints from a controlplane stack.

The values can be generated like:

openstack stack output show controlplane EndpointMap

Or with https://review.openstack.org/#/c/521969/ applied to heatclient:

openstack stack output show controlplane EndpointMap --format yaml \
 | grep -A 1000 output_value | sed "s/^/  /" \
 | sed "1s/^/parameter_defaults:\n  EndpointMapOverride:\n/" | sed "/output_value/d"

Change-Id: Ie1185b99db1b0db93acaf0deae05bd7b707b442f

overcloud.j2.yaml

@@ -63,6 +63,10 @@ parameters:
     default: []
     description: List of extra hosts entries to be appended to /etc/hosts
     type: comma_delimited_list
+  EndpointMapOverride:
+    default: {}
+    description: Can be used to override the calcluated EndpointMap
+    type: json
   ExtraConfig:
     default: {}
     description: |
@@ -353,7 +357,10 @@ resources:
     type: OS::Heat::Value
     properties:
       type: json
-      value: {get_attr: [EndpointMap, endpoint_map]}
+      value:
+        map_merge:
+          - {get_attr: [EndpointMap, endpoint_map]}
+          - {get_param: EndpointMapOverride}
 
   SshKnownHostsConfig:
     type: OS::TripleO::Ssh::KnownHostsConfig
@@ -376,7 +383,7 @@ resources:
       ServiceNetMap: {get_attr: [ServiceNetMap, service_net_map]}
       ServiceData:
         net_cidr_map: {get_attr: [NetCidrMapValue, value]}
-      EndpointMap: {get_attr: [EndpointMap, endpoint_map]}
+      EndpointMap: {get_attr: [EndpointMapData, value]}
       DefaultPasswords: {get_attr: [DefaultPasswords, passwords]}
       RoleName: {{role.name}}
       RoleParameters: {get_param: {{role.name}}Parameters}
@@ -535,7 +542,7 @@ resources:
         properties:
           CloudDomain: {get_param: CloudDomain}
           ServiceNetMap: {get_attr: [ServiceNetMap, service_net_map]}
-          EndpointMap: {get_attr: [EndpointMap, endpoint_map]}
+          EndpointMap: {get_attr: [EndpointMapData, value]}
           Hostname:
             str_replace:
               template: {get_param: {{role.name}}HostnameFormat}
@@ -857,7 +864,7 @@ resources:
         {{role.name}}: {get_attr: [{{role.name}}Servers, value]}
 {% endfor %}
       stack_name: {get_param: 'OS::stack_name'}
-      EndpointMap: {get_attr: [EndpointMap, endpoint_map]}
+      EndpointMap: {get_attr: [EndpointMapData, value]}
       ctlplane_service_ips:
         # Note (shardy) this somewhat complex yaql may be replaced
         # with a map_deep_merge function in ocata.  It merges the