ttcn3-asterisk-ims-ue-test: set execfn
The wrapper_core_bt_on_error.sh should get a backtrace if a coredump
appears. This didn't work because the execfn could not be extracted via
file:
$ file core
core: ELF 64-bit LSB core file, x86-64, version 1 (SYSV), too many program headers (2201)
Add a fallback execfn path so it works in this case too.
Change-Id: Ia6b170b127d6458c3e74b1a32a549b04ae460c75
