added polling_interval for manually approved certificates

[randomizer3000]

certmonger by default rechecks if a certificate has been issued every 7 days (doesnt seem user configurable from their documentation), this is a bit long and it would be nice if this was a configurable value. This PR looks to implement a setting called poll_interval which makes use of the certmonger exit status 5. Default for this PR has been set at 1 hour.

--------- secton from https://pagure.io/certmonger/blob/master/f/doc/helpers.txt

• If the client should wait for a period of time, output a "cookie" value and exit with status 1. The daemon will try again later at a time of its choosing (the default is currently 7 days).
• If the client should wait for a specific period of time (for example, if the CA has told it when to try again), output a delay size in seconds, a newline, and a "cookie" value, and exit with status 5. The daemon will try again after the specified amount of time has passed.

[dmulder]

@randomizer3000 this looks good to me, but could you possibly add a test for this?