Set default disk to non-primary

plugins/kernel_v2/config/disk.rb

@@ -102,9 +102,9 @@ module VagrantPlugins
         @file = nil if @file == UNSET_VALUE
 
         if @primary == UNSET_VALUE
-          @primary = true
-        else
           @primary = false
+        else
+          @primary = true
         end
 
         # Give the disk a default name if unset

test/unit/plugins/kernel_v2/config/disk_test.rb

@@ -43,9 +43,9 @@ describe VagrantPlugins::Kernel_V2::VagrantConfigDisk do
       expect(subject.type).to eq(type)
     end
 
-    it "defaults to primray disk" do
+    it "defaults to non-primray disk" do
       subject.finalize!
-      expect(subject.primary).to eq(true)
+      expect(subject.primary).to eq(false)
     end
   end