extract_utils: Add support for files in rootfs

 * A final "rootfs" tag in the last column will place
   the chosen file into the ramdisk
 * Currently only supports files in /sbin
 * Cleaned up usage of class-specific flags
 * Simplified code

Change-Id: Id823d70aab51f8767522f697eaf65f52fc64b94b
1 file changed