`--s3-bucket` not available for `rain stackset deploy`

[Scribbd]

Related issue: #528

Bug:

It looks like the bucket-commands do not propagate down to subcommands for rain stackset.

> rain stackset deploy --s3-bucket example example
Error: unknown flag: --s3-bucket
Usage:
  rain stackset deploy <template> [stackset] [flags]

Flags:
      --accounts strings         accounts for which to create stack set instances
      [...]

PR

#593

I took a moment to study your change and how the other subcommands implemented their 2nd layer of subcommands that also had the bucket options enabled (ex: rain cc), and implemented this. After compilation it ran as follows:

> ./rain stackset deploy --s3-bucket example example
unable to confirm whether artifact bucket exists: operation error S3: HeadBucket, https response error StatusCode: 301, RequestID: 7PH6C0952GZHQPES, HostID: FnWzbqpQmgkB+pejjPAIFENh63GRcgqdQRxQicEhtvTYIbYpVFKLsUp0G7MwflKR3ikPeDAaqJU=, api error MovedPermanently: Moved Permanently

I can confirm that my binary was able to use our organization bucket.

I acknowledge that Go isn't my forte.

[Scribbd]

With the merge of #593, this issue can be closed.