daemon: Automatically compress our log files

After server startup compress any stale logs which aren't yet
compressed, and then once every 24 hours compress any other logs
that haven't yet been compressed.

This saves disk space for the archived logs, and its useful for us
to do it automatically because most Linux distributions don't know
where our log files are, so they can't automatically compress them
along with other system logs.

WorkQueue needed to be modified to not remove periodic tasks from
the running task list, so the compressor can be seen in the dump
from gerrit show-queue.

Change-Id: I523bfdc0005d8c8112591f3460b799fde9abe123
Signed-off-by: Shawn O. Pearce <sop@google.com>