Set configFromDisk to false after successful configuration
Set configFromDisk to false after successful configuration

Summary:
As soon as we successfully config from disk, bump down the configFromDisk stat.
That allows monitoring the number of current mcrouters that are using stale
configs.

Reviewed By: spalamarchuk

Differential Revision: D4991122

fbshipit-source-id: 6e19003b1f8c7211ce1effd7279abde4f35736bd

facebook/mcrouter,facebook/mcrouter,facebook/mcrouter,facebook/mcrouter