healtd: Send messages to Android log, not the kernel log

If the system doesn't have the expected battery configuration then
healthd is quite noisy with it's log messages during boot and every
minute thereafter. Rather than have this spamming the kernels serial
console, direct this instead to Android's logging system.

This also has the effect of working around a serial port bug on
vexpress: https://bugs.launchpad.net/linaro-android/+bug/1254738
but reducing mostly spurious serial port noise is a good aim in itself.

Change-Id: I0eff5637009cfee47891a9c2363145634cbf0ae1
Signed-off-by: Jon Medhurst <tixy@linaro.org>