Tripswitch for all file access

From a discussion with @jacobvosmaer-gitlab.

We are now relatively confident that all remaining endpoints in GitLab-CE and nearly all remaining endpoints in GitLab-EE have been ported to Gitaly.

A final step in this process is to create a "tripswitch" feature-flag toggle which will error out if any GitLab.com code attempts to access the NFS mount directly, instead of going through Gitaly.

Once this is enabled, we'll be able to determine absolutely whether or not we have reached Gitaly v1.0 (all git access on GitLab.com goes via Gitaly)

This needs to be completed before %11.0 on the 7th of June.

Provisional Plan

  1. 24 May: all remaining Gitaly feature toggles, except those with known issues are enabled on GitLab.com
  2. 7 June: tripswitch ships
  3. 7 June: all encoding bugs fixed: #1208 (closed) #1168 (closed)
  4. 7 June: go-git implementation of FindCommit ships: !691 (merged)
  5. 8 June: All Gitaly endpoints shipped with %11.0 turned on
  6. 8-22 June: continue to ship patches for remaining bugs in Gitaly
  7. 22 June: GitLab %11.0 ships
  8. 23 June: Tripswitch engaged

cc @jacobvosmaer-gitlab @bkc @zj

Edited by Andrew Newdigate