CAS-1182: Configure logging to not disclose plaintext valid TGTs

Patch to address both audit and normal logs. 

Sample output:

```
2014-07-12 04:10:35,033 DEBUG [org.jasig.cas.ticket.registry.DefaultTicketRegistry] - Attempting to retrieve ticket [TGT-********************************************************-cas01.example.org]
2014-07-12 04:10:35,099 DEBUG [org.jasig.cas.CentralAuthenticationServiceImpl] - Removing ticket [TGT-********************************************************-cas01.example.org] from registry.
2014-07-12 04:10:35,101 DEBUG [org.jasig.cas.ticket.registry.DefaultTicketRegistry] - Attempting to retrieve ticket [TGT-********************************************************-cas01.example.org]
2014-07-12 04:10:35,103 DEBUG [org.jasig.cas.CentralAuthenticationServiceImpl] - TicketGrantingTicket [TGT-********************************************************-cas01.example.org] cannot be found in the ticket registry.
2014-07-12 04:10:35,118 DEBUG [org.jasig.cas.audit.spi.TicketOrCredentialPrincipalResolver] - Resolving argument [String] for audit
2014-07-12 04:10:35,120 DEBUG [org.jasig.cas.ticket.registry.DefaultTicketRegistry] - Attempting to retrieve ticket [TGT-********************************************************-cas01.example.org]
2014-07-12 04:10:35,121 DEBUG [org.jasig.cas.audit.spi.TicketOrCredentialPrincipalResolver] - Could not locate ticket [TGT-********************************************************-cas01.example.org] in the registry
2014-07-12 04:10:35,123 DEBUG [org.jasig.cas.audit.spi.TicketOrCredentialPrincipalResolver] - Unable to determine the audit argument. Returning [audit:unknown]
2014-07-12 04:10:35,128 INFO [com.github.inspektr.audit.support.Slf4jLoggingAuditTrailManager] - Audit trail record BEGIN
=============================================================
WHO: audit:unknown
WHAT: TGT-********************************************************-cas01.example.org
ACTION: TICKET_GRANTING_TICKET_DESTROYED
APPLICATION: CAS
WHEN: Sat Jul 12 04:10:35 PDT 2014
CLIENT IP ADDRESS: ...
SERVER IP ADDRESS: ...
=============================================================
```