[automerger skipped] Add boot.img substitution to the build_mixed script. am: aabbd91ab5 -s ours
am: c3e157db5a -s ours
am skip reason: change_id I2877e79522b5836e876c87f38221ca6890c41ce6 with SHA1 aabbd91ab5 is in history

Change-Id: I4b2286ad590cc5a43c2ee1641a4f1baed3e5b9aa