Add optional retries command line arguments to the rpc client

[icook]

This will allow payouts that are attempted infrequeuntly to be automatically retried. Probably want the following options:

1. Retry backoff (number of seconds to wait between retrying)
2. Number of times to retry payout before giving up OR
3. Number of seconds after first attempt to stop retrying (IE, we payout every four hours, so if it is 3.5 hours after first attempt, stop retrying to avoid overlapping runs.)

NOTE: None of the payout code is designed to be properly interleaved (although may still operate properly), so ensuring careful avoidance of concurrent payout script operation is very important!