Bug 6913 - change how ports are handled by koha-create

Bug 6913 - change how ports are handled by koha-create

This does two things:
* Allows OPACPORT to be specified to change the default OPAC port,
* removes the port number from the ServerName directive, as it's already
  handled by the VirtualHost declaration.

Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
(cherry picked from commit 44377378582a1cbe9b38858f81d33dd1480a195d)

Signed-off-by: Chris Nighswonger <chris.nighswonger@gmail.com>