Since we're moving all policy into code and documenting it there we
should generate those docs automatically, so they are less likely to
be out-of-date.
Also add releasenote for ops to aware that Heat is now using
policies in code and their Orchestration service needs to avoid
depends on policy.json file if file not exist, since there is no
such file by default after this patch.
Partially-Implements: bp policy-in-code
Change-Id: I25fc5a110b1fe515918e042f220c23ac9a7e811f
222a8ac5e9