With changes inside Designate merged about policy-incode, there
is no longer a default policy.json file in the venv, so we
need to change how we implement the file, and should only do
so if there is a config override configured for it.
If there is no policy override configured, but a policy.json
file is present, then it's likely left over from a previous
build. To ensure that we do not carry legacy configuration
files which override the policy-in-code we remove the legacy
file. This is done on restart to ensure that the policy still
applies until the code is updated.
Change-Id: Iea4d2029723529444b93d7deca58824e592d0e0f