[automerger skipped] Add a default value for the RBE_log_dir variable. am:...

[automerger skipped] Add a default value for the RBE_log_dir variable. am: 26195be9 am: 38a658c6 -s ours

am skip reason: Change-Id Id93dd80119037b594e5f8c370f4ac2fbc12a5144 with SHA-1 26195be9 is in history

Original change: https://googleplex-android-review.googlesource.com/c/platform/build/soong/+/12447247

Change-Id: I4d4968eeed6e17719f338143c55ae34871c7db32