alertserver: Fix login

BUG=skia:3036
TBR=jcgregorio

Review URL: https://codereview.chromium.org/698643003
alertserver: Fix metadata keys

BUG=skia:3036
TBR=jcgregorio

Review URL: https://codereview.chromium.org/683863005
Primarily this adds login to correctness app using the login packages in the shared go space.

It does a few more things:

- removes all dead code under 'attic'
- add a HTTP endpoint to triage digests
  (WIP, does not work yet, but depends on authentication being in place).

Most, if not all, TODOs will be resolved in the next CL.

BUG=skia:2930

Review URL: https://codereview.chromium.org/683913006