[automerger skipped] Add boot.img substitution to the build_mixed script. am: aabbd91ab5 -s ours am: c3e157db5a -s ours
am: 6f31f9cc2e -s ours
am skip reason: change_id I2877e79522b5836e876c87f38221ca6890c41ce6 with SHA1 aabbd91ab5 is in history

Change-Id: I2a0637ce96830fe575a0efb0f4c807e9c8e178b2