Add support for reading logs extra attrs

The jsonlog logger currently allows specifying envs and labels that
should be propagated to the log message, however there has been no way
to read that back.

This adds a new API option to enable inserting these attrs back to the
log reader.

With timestamps, this looks like so:
```
92016-04-08T15:28:09.835913720Z foo=bar,hello=world hello
```

The extra attrs are comma separated before the log message but after
timestamps.

Without timestaps it looks like so:
```
foo=bar,hello=world hello
```

Signed-off-by: Brian Goff <cpuguy83@gmail.com>
Upstream-commit: bd9d14a07b9f1c82625dc8483245caf3fa7fe9e6
Component: engine

components/engine/docs/reference/api/docker_remote_api.md

@@ -136,6 +136,7 @@ This section lists each version from latest to oldest.  Each listing includes a
 * `POST /auth` now returns an `IdentityToken` when supported by a registry.
 * `POST /containers/create` with both `Hostname` and `Domainname` fields specified will result in the container's hostname being set to `Hostname`, rather than `Hostname.Domainname`.
 * `GET /volumes` now supports more filters, new added filters are `name` and `driver`.
+* `GET /containers/(id or name)/logs` now accepts a `details` query parameter to stream the extra attributes that were provided to the containers `LogOpts`, such as environment variables and labels, with the logs.
 
 ### v1.22 API changes