meta-android: android-system: improve container setup

* setup container rootfs on top of a tmpfs
* mount /system and /vendor correctly as read-only to avoid any modifications
* umount every mounted directory on container stop
* start lxc always with verbose logging to make finding bugs easierd
* requires now lxc >= 1.0

Signed-off-by: Simon Busch <morphis@gravedo.de>