Feature/filestorage sharenetworks delete (#122)

* sfs: Add delete for share networks

* sfs: Make name and descr required for creating share network

* sfs: Add acceptance test for share network Delete

* sfs: Remove required parameters

After taking a close look at the code it appeared that 'name'
and 'description' are not required parameters
diff --git a/openstack/sharedfilesystems/v2/sharenetworks/results.go b/openstack/sharedfilesystems/v2/sharenetworks/results.go
index 9a2891a..946ddd8 100644
--- a/openstack/sharedfilesystems/v2/sharenetworks/results.go
+++ b/openstack/sharedfilesystems/v2/sharenetworks/results.go
@@ -50,3 +50,8 @@
 type CreateResult struct {
 	commonResult
 }
+
+// DeleteResult contains the response body and error from a Delete request.
+type DeleteResult struct {
+	gophercloud.ErrResult
+}