Only create the nested ds stemcell when needed

We don't need to create that stemcell before running any of the
lifecycle specs only the spec that cares about the nested datacenter

[#103949760](https://www.pivotaltracker.com/story/show/103949760)

Signed-off-by: Jonathan Barnes <[email protected]>

src/vsphere_cpi/spec/integration/lifecycle_spec.rb

@@ -59,8 +59,6 @@
       raise "Corrupt image, tar exit status: #{$?.exitstatus} output: #{output}" if $?.exitstatus != 0
       cpi = described_class.new(cpi_options)
       @stemcell_id = cpi.create_stemcell("#{temp_dir}/image", nil)
-      nested_ds_cpi = described_class.new(@nested_datacenter_cpi_options)
-      @nested_datacenter_stemcell_id = nested_ds_cpi.create_stemcell("#{temp_dir}/image", nil)
     end
   end
 
@@ -101,8 +99,6 @@ def cpi_options(options = {})
   after(:all) {
     cpi = described_class.new(cpi_options)
     cpi.delete_stemcell(@stemcell_id) if @stemcell_id
-    nested_datacenter_cpi = described_class.new(@nested_datacenter_cpi_options)
-    nested_datacenter_cpi.delete_stemcell(@nested_datacenter_stemcell_id) if @nested_datacenter_stemcell_id
   }
 
   def vm_lifecycle(disk_locality, resource_pool, network_spec, stemcell_id = @stemcell_id)
@@ -338,8 +334,17 @@ def clean_up_vm_and_disk(cpi)
 
       let(:vlan) { @nested_datacenter_vlan }
 
+      before do
+        Dir.mktmpdir do |temp_dir|
+          output = `tar -C #{temp_dir} -xzf #{@stemcell_path} 2>&1`
+          raise "Corrupt image, tar exit status: #{$?.exitstatus} output: #{output}" if $?.exitstatus != 0
+          @nested_datacenter_stemcell_id = cpi.create_stemcell("#{temp_dir}/image", nil)
+        end
+      end
+
       after do
         clean_up_vm_and_disk(cpi)
+        cpi.delete_stemcell(@nested_datacenter_stemcell_id) if @nested_datacenter_stemcell_id
       end
 
       it 'exercises the vm lifecycle' do