Domain scanning time reduced significantly

@krasio noted that the time taken to scan our pages configuration for gitlab.io reduced significantly on the 19th September: https://log.gitlab.net/goto/a87e3399d7ff8f5aac42b0a2cfde7e67

Why this has happened is not certain. Perhaps it's an unalloyed good thing caused by the upgrade of a dependency (godirwalk for instance), in which case this issue can just be closed.

Another possibility is that configuration scanning time is affected by uptime - the longer a pages process is up, the longer the scan takes, perhaps? If that's the case, it's likely to be a resource leak of some sort and we should investigate.

First step: check back in a week. If scanning is taking significantly more than 5 minutes, that lends weight to theory 2.

Number of domains in the scan has not changed significantly.