[1/3] Install persistence support

Copy files from OUT/install to ZIP/install and extract to /tmp/install
at install time.  This is an extensible framework that may be used for
other install tasks as needed.  Note that none of the install files are
only extracted to a ramdisk, they are never written to /system.

Run script persist.sh with argument "save" prior to formatting /system
and again with argument "restore" after /system is installed.  This may
be explicitly disabled by setting "TARGET_DISABLE_PERSIST := true".

Change-Id: I8b3b298e3c43b31aa275c3cb5d2eeae4cd33760b