Deleting and re-adding tenant raises exception (and fails)

1. As administrator, delete a tenant.
2. Attempt to add a new tenant identical to the deleted one.

Tenant isn't added and server error message is as below

```
[2013-11-05T18:59:01.068Z] ERROR: oae/10003 on lawn-143-215-205-120.lawn.gatech.edu: An uncaught exception was raised to the application.
    TypeError: Cannot read property 'alias' of null
        at Object.module.exports.getStrategyId (/Users/stephen/Documents/Software/oae/Hilary/node_modules/oae-authentication/lib/util.js:81:39)
        at /Users/stephen/Documents/Software/oae/Hilary/node_modules/oae-authentication/lib/api.js:674:55
        at Function._.each._.forEach (/Users/stephen/Documents/Software/oae/Hilary/node_modules/underscore/underscore.js:87:22)
        at module.exports.refreshStrategies (/Users/stephen/Documents/Software/oae/Hilary/node_modules/oae-authentication/lib/api.js:672:7)
        at EventEmitter.ConfigAPI.on.log.error.tenantAlias (/Users/stephen/Documents/Software/oae/Hilary/node_modules/oae-authentication/lib/api.js:48:5)
        at EventEmitter.emit (events.js:95:17)
        at /Users/stephen/Documents/Software/oae/Hilary/node_modules/oae-tenants/lib/api.js:66:17
        at /Users/stephen/Documents/Software/oae/Hilary/node_modules/oae-tenants/lib/api.js:184:9
        at /Users/stephen/Documents/Software/oae/Hilary/node_modules/oae-util/lib/cassandra.js:755:9
        at onReturn (/Users/stephen/Documents/Software/oae/Hilary/node_modules/helenus/lib/connection.js:453:7)
[2013-11-05T18:59:01.070Z] ERROR: oae-authentication/10003 on lawn-143-215-205-120.lawn.gatech.edu: Error fetching tenant to update authentication configuration. (tenantAlias=Tenant)
```