logd: throttle SELinux denials to 20/sec

Impose a limit of 20 selinux denials per second. Denials beyond
that point don't add any value, and have the potential to cause
crashes or denial of service attacks.

Do some other misc cleanup while I'm here.

Bug: 18341932
Change-Id: I6125d629ae4d6ae131d2e53bfa41e1f50277d402
healthd: Reinitialize mChargerNames for every battery update

Booting up the device without the usb sets the usb power supply
type as UNKNOWN. Due to this mChargerNames gets incorrectly
initialized at bootup. The value of usb power supply type changes
at run-time. So it makes sense to update mChargerNames everytime
we have a battery related update.

Change-Id: I2ec9f9a420ca61814d43c316b418ce94de3691bc