[automerger skipped] Don't use mainline prebuilts for coverage builds. am:...

[automerger skipped] Don't use mainline prebuilts for coverage builds. am: 94518417 am: e8f75691 -s ours

am skip reason: Merged-In Id29e273c1df1fa27a038ebdcff1a17acca58bd46 with SHA-1 31167aea is already in history

Original change: https://android-review.googlesource.com/c/platform/build/+/1784567

Change-Id: I16c2a1833ebd1dac3007237a479db6c97d2a14aa