Why? HttpCheck/HttpsCheck are examples of rule checks
that can be implemented outside of the oslo.policy
library. Once we setup the infra for registering and
using these as stevedore extensions, we automatically
get the capability of other folks contributing to
writing custom rules for their own use cases.
* Add HttpCheck/HttpsCheck as entrypoints in setup.cfg
* parser will check get_extensions() to see if there
are any external checks registered
* Move HttpCheck/HttpsCheck into external module
* Move related test cases to test_external.py
Change-Id: Icde2b26a38d7c7842defae053228d9208454b969