When fernet key rotations are done via the mistral action, the action
will check the KeystoneFernetMaxActiveKeys and and purge the excess keys
from the mistral environment or swift container. If the parameter is not
present, a default value of 5 is taken. And if for some reason the user
gives a smaller value, a minimum of 3 is taken into account.
bp keystone-fernet-rotation
Depends-On: I9c6b0708c2c03ad9918222599f8b6aad397d8089
Change-Id: I4a28073c93c210703871daa8fe660fc1914464e8