logger: introduce lazy/hybrid approach to early logging

logger: introduce lazy/hybrid approach to early logging

This mode is introduced in an attempt to limit CPU usage during boot time.
The logger will now wake up exactly after (instead of up to) the epoll delay
for some configurable amount of time (by default 10s). Ideally this would
just be waiting on BootingDone but the daemon doesn't handle DBus yet, which
would be a larger undertaking. After that delay, it switches back to usual
epoll behaviour (waking up on each log, limiting log loss).

Change-Id: I55555978902d18b2d922663a24fe1caeb6d330e8
Signed-off-by: Michal Bloch <m.bloch@samsung.com>