scalar: configure maintenance during 'reconfigure'

scalar: configure maintenance during 'reconfigure'

The 'scalar reconfigure' command is intended to update registered repos
with the latest settings available. However, up to now we were not
reregistering the repos with background maintenance.

In particular, this meant that the background maintenance schedule would
not be updated if there are improvements between versions.

Be sure to register repos for maintenance during the reconfigure step.

Signed-off-by: Derrick Stolee <stolee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>