Adding /data/local/traces for traceur app

Traceur app is being split out of shell user. Previously it logged to
shell's bugreports directory. It no longer has access, so it needs a
new, user-friendly file location to store trace data.

Bug:68126425
Test: Traceur can write and shell can read from this directory
Change-Id: I9e344973fd43eb5699f7a848524e20b06458fb77