Ensure /data/adb exists

Ensure that /data/adb always exists. This directory is used
for writing adb debugging information when persist.adb.trace_mask
is set.

Bug: https://code.google.com/p/android/issues/detail?id=72895
Change-Id: I9cee2a0202417ff72a5ede7742e25877f51732dd
Merge "Ensure /data/adb exists"