The original MR [1] fixed red specs for Rails 5.
But while the failed specs were fixed, that changes brought new failed
specs which weren't caught up in [1].

This commit just fixes the fix. :)

New errors are like these:

```
Failed to upgrade to WebSocket (REQUEST_METHOD: GET, HTTP_CONNECTION: keep-alive, HTTP_UPGRADE: )
Finished "/-/boards/1/lists"[non-WebSocket] for 127.0.0.1 at 2018-06-20 18:09:26 +0200
```

[1]: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/20015

Since Rails 5.0 the new framework has been added. It's called ActionCable.
It brings WebSockets support to rails applications.
By default the mountpoint of WebSocket requests is `/cable` [1].

GitLab allows using top level names as namespaces or usernames.
For example, `gitlab.com/cable` at this moment leads to a user with the
nickname `cable`.

This commit changes ActionCable's mountpoint to a reserved top level
word `-`.
This is just a stub and should not be be used in real work.

Please set correct mountpoints for each environments when configuring
ActionCable for real using.

[1]: https://github.com/rails/rails/blob/5-0-stable/actioncable/lib/action_cable.rb#L38

Update the monkey-patch to make it work in Rails 5.

Use data_source_exists? where possible instead of table_exists? in order to be Rails5 compatible

It fixes Rails 5.0 deprecation flooding like:

```
DEPRECATION WARNING: Passing strings or symbols to the middleware builder is deprecated, please change
them to actual class references.  For example:

  "::Gitlab::Middleware::ReadOnly" => Gitlab::Middleware::ReadOnly

 (called from <top (required)> at /builds/gitlab-org/gitlab-ce/config/environment.rb:11)
DEPRECATION WARNING: Passing strings or symbols to the middleware builder is deprecated, please change
them to actual class references.  For example:

  "ActionDispatch::Static" => ActionDispatch::Static

 (called from <top (required)> at /builds/gitlab-org/gitlab-ce/config/environment.rb:11)
DEPRECATION WARNING: Passing strings or symbols to the middleware builder is deprecated, please change
them to actual class references.  For example:

  "Gitlab::Testing::RequestBlockerMiddleware" => Gitlab::Testing::RequestBlockerMiddleware

 (called from <top (required)> at /builds/gitlab-org/gitlab-ce/config/environment.rb:11)
DEPRECATION WARNING: Passing strings or symbols to the middleware builder is deprecated, please change
them to actual class references.  For example:

  "ActionDispatch::Static" => ActionDispatch::Static

 (called from <top (required)> at /builds/gitlab-org/gitlab-ce/config/environment.rb:11)
DEPRECATION WARNING: Passing strings or symbols to the middleware builder is deprecated, please change
them to actual class references.  For example:

  "Gitlab::Testing::RequestInspectorMiddleware" => Gitlab::Testing::RequestInspectorMiddleware

 (called from <top (required)> at /builds/gitlab-org/gitlab-ce/config/environment.rb:11)
```

Resolve "[Rails5] `ActionView::MissingTemplate` in spec/features/projects/wiki/user_views_wiki_page_spec.rb"

Issuing a SIGUSR2 to a unicorn involves a dance where new workers are
spun up before the old ones are shut down. To ensure Prometheus
.db files aren't deleted after the new workers are shut down, we
need to clean these files up before the unicorn process is run.

Relates to https://gitlab.com/gitlab-org/omnibus-gitlab/merge_requests/2582

In Rails 5 IndexDefinition contains also `:comment` attribute.

Enforce UTF-8 encoding on user input in LogrageWithTimestamp formatter and filter out file content from logs

We have a number of import errors occurring with 422 errors, and
it's hard to determine why they are happening. This change will
surface the errors in the log lines.

Relates to #47365

- All definitions have been replaced by classes:
  http://graphql-ruby.org/schema/class_based_api.html
- Authorization & Presentation have been refactored to work in the
  class based system
- Loaders have been replaced by resolvers
- Times are now coersed as ISO 8601

`#send_file` won't properly set the favicon's content type otherwise.

attr_encrypted does different things with `key` depending on what mode you are using:

1. In `:per_attribute_iv_and_salt` mode, it generates a hash with the salt:
https://github.com/attr-encrypted/encryptor/blob/c3a62c4a9e74686dd95e0548f9dc2a361fdc95d1/lib/encryptor.rb#L77.
There is no need to truncate the key to 32 bytes here.

2. In `:per_attribute_iv` mode, it sets the key directly to the password, so
truncation to 32 bytes is necessary.

Closes #47166

[ci skip]