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

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: Icf559f9c8b37c6f564c820fde79c85a77ba4f839

doc/source/_exts/projects.py

@@ -38,4 +38,4 @@ def setup(app):
     filename = os.path.abspath('reference/projects.yaml')
     app.info('reading %s' % filename)
     with open(filename, 'r') as f:
-        _projects_yaml = yaml.load(f.read().decode('utf-8'))
+        _projects_yaml = yaml.safe_load(f.read().decode('utf-8'))

tools/teamstats.py

@@ -252,7 +252,7 @@ class ValidateSingleVendor(base.ValidatorBase):
 def main():
     filename = os.path.abspath('reference/projects.yaml')
     with open(filename, 'r') as f:
-        projects = [k for k in yaml.load(f.read())]
+        projects = [k for k in yaml.safe_load(f.read())]
         projects.sort()
     print '<Team> (top commit % | top review % | top core review % | ' \
         'top core reviewer %)'

tools/validate_tags.py

@@ -47,7 +47,7 @@ def main():
     if not os.path.isfile(filename):
         sys.exit("Projects.yaml was not found at %s" % (filename))
     with open(filename, 'r') as f:
-        teams = yaml.load(f.read())
+        teams = yaml.safe_load(f.read())
     for team in teams:
         # Check team based tags
         for validator in team_validators: