While I do not agree with _every_ style change, this will force Dokku to have consistent formatting across all shell scripts, which is arguably a Good Thing™.
The command used to reprocess everything is:
```shell
shfmt -l -bn -ci -i 2 -w .
```
- expose an nginx:validate command that can be used to show validation information
- properly reference the invalid nginx config, rather than tell the user that another app's nginx config is invalid when deploying their own app
- allow a user to cleanup bad nginx config files out of band when they are blocking a deploy _without_ requiring knowing where that nginx config is
Note that this may have issues with generated nginx.conf files that depend on other apps or other parts of the nginx config. For now, this is acceptable, though it is something that needs to be field tested.
Closes#3162
This avoids cases where a developer believes they should be able to provision an nginx proxy but is unable to as no web process is configured to listen for the app.
Also silence stderr when extracting custom nginx templates. If there is stderr, that means we were not able to retrieve the template, but it's of no consequence for debugging.
Closes#3262
The centos rpm packages should be installable on centos once this is merged and released. However, Dokku will not maintain an Rhel-specific repository as there is no way for us to feasibly test it.
Closes#3046
`SSL_SERVER_NAME` should contain items found in the ssl certs
(E.G. CommonName and AltNames), but not already in the `NOSSL_SERVER_NAME`
list. That will avoid the dups in the `nginx.conf` and kill the warning
initially cited in dokku/dokku#2474
Certain versions of nginx have bugs that prevent HTTP/2 from properly responding to all clients, thus causing applications to be unavailable.
Closes#2435
Newer versions of nginx drop spdy support in favor of http2, and thus the nginx config that we bundle with dokku causes nginx to fail to reload in certain cases. This change drops spdy support in favor of http2 for versions of nginx greater than 1.9.5.
Closes#2216
