afdo: refactoring to support multiple source of profiles

Instead of hard-coded names everywhere, now profiles are specified in
two dictionaries.

BUG=chromium:829170
TEST=afdo_unittest, afdo_stages_unittest
     cros tryjob master-chromium-pfq-tryjob chell-chrome-pfq-tryjob
CQ-DEPEND=CL:1008263

Change-Id: I8f8b6abad84e475fd338f0fc4c2903fde7d7c9f3
Reviewed-on: https://chromium-review.googlesource.com/1008282
Reviewed-by: Luis Lozano <llozano@chromium.org>
Tested-by: Ting-Yuan Huang <laszio@chromium.org>
Commit-Queue: Ting-Yuan Huang <laszio@chromium.org>
6 files changed