change /data/bugreports to /bugreports

It's 5 characters shorter, has no runtime costs, can be stored on a
read-only partition, and avoids problems like b/27262109 and b/27204904.
It allows makes some security hardening easier.

Bug: 27262109
Bug: 27204904
Bug: 32799236
Test: verified new symlink created and old one not present
Change-Id: Ief362e13569ad9c868a7f0f9c4dbd6a328c96c6b