set ServiceClient field to nil before unmarshaling (#59)

diff --git a/openstack/compute/v2/servers/testing/requests_test.go b/openstack/compute/v2/servers/testing/requests_test.go
index 6d792d5..b651b92 100644
--- a/openstack/compute/v2/servers/testing/requests_test.go
+++ b/openstack/compute/v2/servers/testing/requests_test.go
@@ -89,6 +89,22 @@
 	th.CheckDeepEquals(t, ServerDerp, *actual)
 }
 
+func TestCreateServerWithImageNameAndFlavorName(t *testing.T) {
+	th.SetupHTTP()
+	defer th.TeardownHTTP()
+	HandleServerCreationSuccessfully(t, SingleServerBody)
+
+	actual, err := servers.Create(client.ServiceClient(), servers.CreateOpts{
+		Name:          "derp",
+		ImageName:     "cirros-0.3.2-x86_64-disk",
+		FlavorName:    "m1.tiny",
+		ServiceClient: client.ServiceClient(),
+	}).Extract()
+	th.AssertNoErr(t, err)
+
+	th.CheckDeepEquals(t, ServerDerp, *actual)
+}
+
 func TestDeleteServer(t *testing.T) {
 	th.SetupHTTP()
 	defer th.TeardownHTTP()