Replaces yaml.load() with yaml.safe_load()

Yaml.load() return Python object may be dangerous if you receive a YAML
document from an untrusted source such as the Internet. The function
yaml.safe_load() limits this ability to simple Python objects like integers or
lists.

Reference:
https://security.openstack.org/guidelines/dg_avoid-dangerous-input-parsing-libraries.html

Change-Id: Iea14d26e6937472d1ac4b8f441bd59c959d2deb0

transform.py

@@ -60,7 +60,7 @@ class LocalResolver(jsonschema.RefResolver):
 
 
 def main():
-    mapping = yaml.load(open('service-types.yaml', 'r'))
+    mapping = yaml.safe_load(open('service-types.yaml', 'r'))
 
     mapping['version'] = datetime.datetime.utcnow().isoformat()
     mapping['sha'] = subprocess.check_output(