Previously, the preview server docker image was based on Debian 8
(jessie). Recently, `jessie-updates` and `jessie-backborts` were removed
from the Debian mirrors ([more info][1]), thus breaking new builds of
the image.
Instead of updating `/etc/apt/sources.list` to remove the obsolete
sources, this commit upgrades to Debian 9 (stretch).
(The GCE VM running the preview server docker container was also
upgraded from Debian 8 to 9 this morning.)
---
Other changes:
- Removed dependency on `chkconfig`, which is not supported on Debian 9.
- Installing `nginx` from the regular repositories (instead of
`*-backports).
- Upgraded to `pm2` v3, which can handle hooking itself up to system
startup better (without `chkconfig` - see above).
- Updated tests to reflect the fact that `nginx` has dropped the reason
phrase in response status lines for HTTP/2 (in compliance with
[the spec][2]). (HTTP/1.1: `HTTP/1.1 200 OK` | HTTP/2: `HTTP/2 200`)
[1]: https://www.lucas-nussbaum.net/blog/?p=947
[2]: https://http2.github.io/http2-spec/#rfc.section.8.1.2.4
PR Close#29976
2f1a862b83