Fix login on Sandstorm by not creating welcome boards

This one is a pretty strange chain of events:

* fetching /.sandstorm-login via accounts-sandstorm's rendezvous protocol
  causes a user to be created in the users collection
* models/users.js has hooks to create a board and lists when a user is created
* models/activities.js has a hook to create activity entries when a list is
  created
* this hook does not handle not having no boardId, which results in attempting
  to run the hook with boardId: 'false'.  'false' does not have a title
  attribute, which causes the whole method call to throw an exception.
* This makes the initial login fail.

While there may be other bugs, the simple fix is to not create the board and
lists when running under Sandstorm, where you only have one board anyway.

models/users.js

@@ -1,3 +1,7 @@
+// Sandstorm context is detected using the METEOR_SETTINGS environment variable
+// in the package definition.
+const isSandstorm = Meteor.settings && Meteor.settings.public &&
+                    Meteor.settings.public.sandstorm;
 Users = Meteor.users;
 
 Users.attachSchema(new SimpleSchema({
@@ -394,24 +398,26 @@ if (Meteor.isServer) {
     return fakeUserId.get() || getUserId();
   };
 
-  Users.after.insert((userId, doc) => {
-    const fakeUser = {
-      extendAutoValueContext: {
-        userId: doc._id,
-      },
-    };
-
-    fakeUserId.withValue(doc._id, () => {
-      // Insert the Welcome Board
-      Boards.insert({
-        title: TAPi18n.__('welcome-board'),
-        permission: 'private',
-      }, fakeUser, (err, boardId) => {
-
-        ['welcome-list1', 'welcome-list2'].forEach((title) => {
-          Lists.insert({ title: TAPi18n.__(title), boardId }, fakeUser);
+  if (!isSandstorm) {
+    Users.after.insert((userId, doc) => {
+      const fakeUser = {
+        extendAutoValueContext: {
+          userId: doc._id,
+        },
+      };
+
+      fakeUserId.withValue(doc._id, () => {
+        // Insert the Welcome Board
+        Boards.insert({
+          title: TAPi18n.__('welcome-board'),
+          permission: 'private',
+        }, fakeUser, (err, boardId) => {
+
+          ['welcome-list1', 'welcome-list2'].forEach((title) => {
+            Lists.insert({ title: TAPi18n.__(title), boardId }, fakeUser);
+          });
         });
       });
     });
-  });
+  }
 }