Better handling of ramdisk during make

make clobber used to call rm -rf out/
so if out is a soft link to i.e. /tmp/out
the soft link is deleted instead the content
so i changed the makefile to rm -rf out/*

Change-Id: Id1991161617da8ec34307a30412c134e31f589b4
fix up ota_from_target_files symlink detection.