fenet keys and docker image/container

[AlvaroVega]

It seems fernet keys are fixed at image creation.

Once a day docker container is rotating fernet keys.

Some problems in HA balanced scenarios could happend if nodes does not share fernet keys or uses sticky sessions.

https://docs.openstack.org/keystone/pike/admin/identity-fernet-token-faq.html

How enable sticky sessions: https://thisinterestsme.com/haproxy-sticky-sessions/
A workaround could be not rotate fernet keys by default.

[AlvaroVega]

Doc about this issue was added in https://github.com/telefonicaid/fiware-keystone-spassword#fernet-keys-and-ha