Support for storing OAT files in app directory

In installPackageLI, dexopt is now performed on a staging directory of the app
(dexopt phase 1). For each codepath:
 - /oat/<isa> directory is created
 - dexopt output goes to the newly created directory. Optimized files have
   .odex extension.

Bug: 19550105
Change-Id: Iec59790d97837b78af82b079fd1970de3388c91d