Make the SSL port configuration explicit, instead of deriving it
from the non-SSL port, but retain the existing functionality in
case anyone depends on it.

The change starts the HTTPS and HTTP connectors separately, so
that it's possible to use independent ports for each. For that to
work, the initialization of the server needs to be shuffled around
a bit. The change also makes it so the initialization of both
connectors is similar, and end up using the same Scheduler - previously
only the HTTP connector would use the correct one.

Also fixed some outdated documentation about a couple of services
that were removed long ago.

Tested with unit tests and by running spark-shell with SSL configs.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #16625 from vanzin/SPARK-17874.