Standby and follower seeding encrypts key files

[jtuttle]

When seeding standbys and followers in production it's best to encrypt the key files on the master before generating seeds so that the keys from the seed are encrypted when copied to the standby / follower. The encrypted keys can be added to the keyring before configuration by adding evoke keys exec to the configuration command, i.e.:

evoke keys exec -m /conjur_files/master-key -- evoke configure standby

We should update the demo to follow this best practice.