[BUGFIX] Reintroduce support for reverseProxySSL

[BUGFIX] Reintroduce support for reverseProxySSL

Creating a backend request relies on TYPO3_CONF_VARS which
is not set yet.
This breaks requests when using a reverse proxy for SSL
because HTTP is used as scheme even thogh HTTPS should be used.

Change-Id: Id3f5fe2189f5bcc017da8ebcc21cc43920917aa0
Resolves: #70525
Releases: master
Reviewed-on: https://review.typo3.org/44001
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Reviewed-by: Helmut Hummel <helmut.hummel@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>