ListBucket SPIKES in collector

[mikegrima]

The S3 ListBuckets call will spike in the collector when there are frequent bucket events that occur.

ListBuckets is an expensive call to AWS, and we will need to significantly reduce the number of times it is called.

Things that need to be done:

1. Need to pass in a session name to cloudaux so that the S3 collector function's ListBucket call is visible in CloudTrail.
2. On collection events, check if the S3 bucket already exists in the current table. If it does, then DO NOT attempt to get the bucket creation date (which calls ListBuckets under the hood). Instead, grab the existing creation and reuse it. If it doesn't -- then the bucket is brand new and we need to grab the creation date.

While spikes in bucket creation can still spam ListBuckets, it will massively reduce the number of calls to that API whenever buckets are modified. Thus a major win.