Log router boot durations

Log the number of seconds it takes a router to boot and accept its first
configuration.

Change-Id: Ie42beb3166e93f93bac71121e1e5e10296aaaa96
fix flake8 issues

Change-Id: I3912c9af919cc4c62a70b9c62327ac06399d8d81
Merge pull request #154 from dhellmann/feature/log-router-boot-time

Log router boot durations