[Reviewer: Matt] Honour /etc/clearwater/config settings for Sprout's S-CSCF port

Matt,

Sprout's S-CSCF port is configurable with "scscf=..." in .etc/clearwater/config (see https://github.com/Metaswitch/sprout/blob/dev/debian/sprout.init.d). However, Homestead's init.d file hardcodes 5054, and so may be incompatible.

This change keeps the default as 5054, but honours the scscf setting if it is different.