Add etc/designate/*.yaml to .gitignore

With recent changes to pool manager config, it is common for users to
have a pool.yaml in etc/designate.

Change-Id: I9c852139907c50c96d33eaa62fa6b006c1ff85e8

.gitignore

@@ -52,4 +52,5 @@ doc/build/*
 doc/source/api/*
 api-ref/build/*
 etc/designate/*.conf
+etc/designate/*.yaml
 var/*