Before this patch yaml.Loader was used by the client to create custom
yaql-enabled yaml loader. It is unsfae do to so, because yaml.Loader is
capable of creating custom python objects from specifically constructed
yaml files.
UI parsing functions also fell back to yaml.Loader if
the custom loader was not supplied.
After this patch all yaml load operations are performed with safe
loaders instead.
Change-Id: Id9bb6eabda35522271ec394f8758a974878cbb4b
Closes-Bug: #1586078
cd182ba363