cli_utils: Use yaml.safe_load instead of yaml.load
yaml.load is unsafe (can call arbitrary Python code) and throws a DeprecationWarning these days
Test Plan
tox
Migrated from D1398 (view on Phabricator)
yaml.load is unsafe (can call arbitrary Python code) and throws a DeprecationWarning these days
tox
Migrated from D1398 (view on Phabricator)