ui: Only allow partition creation with a single datacenter setup (#11817)

ui/packages/consul-partitions/app/templates/dc/partitions/index.hbs

@@ -48,7 +48,15 @@ as |route|>
         </h1>
       </BlockSlot>
       <BlockSlot @name="actions">
-          <a data-test-create href="{{href-to 'dc.partitions.create'}}" class="type-create">Create</a>
+{{#if (can 'create partitions')}}
+        <a 
+          data-test-create 
+          class="type-create"
+          href="{{href-to 'dc.partitions.create'}}"
+        >
+          Create
+        </a>
+{{/if}}
       </BlockSlot>
       <BlockSlot @name="toolbar">
       {{#if (gt items.length 0)}}

ui/packages/consul-ui/app/abilities/partition.js

@@ -3,6 +3,7 @@ import { inject as service } from '@ember/service';
 
 export default class PartitionAbility extends BaseAbility {
   @service('env') env;
+  @service('repository/dc') dcs;
 
   resource = 'operator';
   segmented = false;
@@ -12,7 +13,16 @@ export default class PartitionAbility extends BaseAbility {
   }
 
   get canManage() {
-    return this.canCreate;
+    // management currently means "can I write", not necessarily just create
+    return this.canWrite;
+  }
+
+  get canCreate() {
+    // we can only currently create a partition if you have only one datacenter
+    if (this.dcs.peekAll().length > 1) {
+      return false;
+    }
+    return super.canCreate;
   }
 
   get canDelete() {