auth/cephx: share all tickets and connection_secret in initial reply

auth/cephx: share all tickets and connection_secret in initial reply

Previously, we would give the client the auth ticket, like a rbd TGT
(ticket granting ticket), and the client would then ask for all of the
other tickets it wants in a separate message.

Instead, have the client specify which tickets it wants up front and pass
them all at the same time.

Also, generate and share the connection_secret, which will be used for
encryption.

Signed-off-by: Sage Weil <sage@redhat.com>