Refactor logging.

Refactor logging.

Keep a <component>.lock on the master for all updates, instead of trying
to lock individual directories.

There was a race in static-master-update-component, where we would keep
locks of <component> and <component>-updating.incoming-XXXXXX, and then
move <component> aside and replace it by
<component>-updating.incoming-XXXXXX in two steps.  Things could fail
if in between these two moves, another static-master-update-component
job showed up, and created a new <component> dir.