When running OpenWrt within KVM KEY_POWER is generated from the ACPI
button driver when restarting or powering down the VM.

Extend button-hotplug to allow user space handlers for these events.

Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
Patchwork: http://patchwork.openwrt.org/patch/3799/

SVN-Revision: 37160