ttcn3.sh: add getopts

Add getopts parsing. The idea was to add support for setting a different
IMAGE_SUFFIX argument, but later on it became clear it is not worth
implementing here. Add the getopts logic anyway because it can be used
to add other arguments in the future.

Change-Id: If55a982d92b2a24a175ab7f3a8f048f054033dc2
1 file changed