Redo the logic around showing namespaces

Don't show namespaces if the only namespace is `default`

ui/app/controllers/jobs/job/index.js

@@ -4,6 +4,7 @@ import Sortable from 'nomad-ui/mixins/sortable';
 const { Controller, computed, inject } = Ember;
 
 export default Controller.extend(Sortable, {
+  system: inject.service(),
   jobController: inject.controller('jobs.job'),
 
   queryParams: {

ui/app/services/system.js

@@ -28,6 +28,11 @@ export default Service.extend({
     return this.get('store').findAll('namespace');
   }),
 
+  shouldShowNamespaces: computed('namespaces.[]', function() {
+    const namespaces = this.get('namespaces').toArray();
+    return namespaces.length && namespaces.some(namespace => namespace.get('id') !== 'default');
+  }),
+
   activeNamespace: computed('namespaces.[]', {
     get() {
       const namespaceId = window.localStorage.nomadActiveNamespace || 'default';

ui/app/templates/components/gutter-menu.hbs

@@ -5,7 +5,7 @@
         Workload
       </p>
       <ul class="menu-list">
-        {{#if system.namespaces.length}}
+        {{#if system.shouldShowNamespaces}}
           <li>
             <div class="menu-item">
               {{#power-select

ui/app/templates/jobs/job/index.hbs

@@ -20,7 +20,7 @@
       <div class="boxed-section-body">
         <span><strong>Type:</strong> {{model.type}} | </span>
         <span><strong>Priority:</strong> {{model.priority}} </span>
-        {{#if model.namespace}}
+        {{#if (and model.namespace system.shouldShowNamespaces)}}
           <span> | <strong>Namespace:</strong> {{model.namespace.name}}</span>
         {{/if}}
       </div>