Now KCT can read from the registration section of the scenario.yml file the value 'ua'.
If this is set (and registration is set to yes), KCT will add in the registration xml files
meant for SIPP the header 'User Agent' with the value specified.
To demonstrate how it works the scenario invite_callforward has also been extended and
now it sends registrations with User-Agent: KCT SIPP, additionally it enables feature ua_reject_missing
to check if this header is present and also tests if in the sems loop the ua_reject_missing
is ignored (whitelisting sems).
Change-Id: I709a0e0c3532b8e5246834dc3566b26e95b5f3be
Alessio Garzi