Lazy load StorageManagers upon volume creation

When creating a new volume user has to pick what StorageManager is volume
supposed to be created with, hence we perform API request to fetch those.
Problem is we share angular controller with other volume operations (attach,
detach) that don't need this list of all managers and fetching those
anyway results in permission denied error due to fine-grained permission
setting.

For example if we give user only permission to attach/detach volume, but
not to view StorageManagers, then we must not perform the API call as it
results in 403 with red popup.

With this commit we refactor controller so that it now only performs the
API call "fetch storage managers" when we're creating a new volume, and
not just always by default.

BZ: https://bugzilla.redhat.com/show_bug.cgi?id=1571224

Signed-off-by: Miha Pleško <miha.plesko@xlab.si>

app/assets/javascripts/controllers/cloud_volume/cloud_volume_form_controller.js

@@ -21,18 +21,17 @@ ManageIQ.angular.app.controller('cloudVolumeFormController', ['miqService', 'API
     vm.newRecord = cloudVolumeFormId === 'new';
 
     miqService.sparkleOn();
-    API.get('/api/providers?expand=resources&attributes=id,name,supports_block_storage&filter[]=supports_block_storage=true')
-      .then(getStorageManagers)
-      .catch(miqService.handleFailure);
 
     if (cloudVolumeFormId !== 'new') {
       // Fetch cloud volume data before showing the form.
       API.get('/api/cloud_volumes/' + cloudVolumeFormId + '?attributes=ext_management_system.type,availability_zone.ems_ref,base_snapshot.ems_ref')
         .then(getCloudVolumeFormData)
         .catch(miqService.handleFailure);
     } else {
-      // Initialise the form immediately when creating a new volume.
-      setForm();
+      // Fetch StorageManagers that we can even create the new volume for.
+      API.get('/api/providers?expand=resources&attributes=id,name,supports_block_storage&filter[]=supports_block_storage=true')
+        .then(getStorageManagers)
+        .catch(miqService.handleFailure);
     }
   };
 
@@ -219,6 +218,8 @@ ManageIQ.angular.app.controller('cloudVolumeFormController', ['miqService', 'API
     if (storageManagerId) {
       vm.storageManagerChanged(vm.cloudVolumeModel.storage_manager_id);
     }
+
+    setForm();
   };
 
   var getCloudVolumeFormData = function(data) {