init.iago.rc: manually start class late_start

The class late_start is started after the mount_all statement.
However, in live mode the mount_all was removed (from init.common.rc).
Thus the sdcard service is not started.

Change-Id: I3ccc7a0163e0689a30e98b40d76bce0a6b4649cd
preinit: support ext2/ext3/ext4 and images in a subfolder

The features are added to preinit:
* Search installmedia in ext2/ext3/ext4 partitions
* Allow images being put in a subfolder same as kernel or specified by SRC in cmdline

Change-Id: I41277d0227e2c8ae59426465ba4d94e208285a1d