auth: CryptoKey, use dynamic usage keys

auth: CryptoKey, use dynamic usage keys

Use new extended api to implement non-zero usage constants.

3 std::string connection_secret
4 CephXServiceTicket
5 encode(CephXTicketBlob)
10 CephXServiceTicketInfo
11 CephXAuthorize
13 CephXAuthorizeChallenge
15 CephXAuthorizeReply
16 RotatingSecrets

Generally speaking, these keys are constructed by
"CryptoKey::decode" which does not know the context for how the
key will be used, so usage can't be set here.  In a brief
experiment, these usages for keys were invoked by keys decoded
under these routines:
3 4 5		CephxClientHandler::handle_response
11 13 15	CephXTicketHandler::verify_service_ticket_reply

Signed-off-by: Marcus Watts <mwatts@redhat.com>