Correct file is policy.yaml and only needed if overriding defaults. This
only warns if the file is present in case it was left by a previous
version and not actually needed or used.
Also checks for the policy_file being overridden in config, and if so,
warns if the specified file does not exist.
Change-Id: Ia46e843ad245cf8263b97b773fac9bc6c6fe6647
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>