Add idempotent check to sqs.Delete actor
Fail sqs.Delete in dry mode w/out idempotent flag.
Add required parameter to WaitUntilEmpty
Update sqs.Delete documentation
Update sqs.WaitUntilEmpty documentation
Ensure that ActorException is raised.

* Move error message to be part of exception instead of separate log.
Merge pull request #91 from Nextdoor/fix_delete

Add idempotent check to sqs.Delete actor
Merge pull request #92 from Nextdoor/sqs_wait

Add required parameter to WaitUntilEmpty
Merge branch 'master' of github.com:Nextdoor/kingpin into issue_97_proposal
Fix SQS unit tests after execute() exception handling change.