fix test_prefixreg to actually get the FaceID using the newly introduced ccnbx command.
fix test_prefixreg to actually get the FaceID using the newly introduced ccnbx command.

refs #91  Registration protocol in ccnd

ebollens/ccnmp,ebollens/ccnmp,cawka/ndnx,cawka/ndnx,cawka/ndnx,svartika/ccnx,svartika/ccnx,svartika/ccnx,svartika/ccnx,ebollens/ccnmp,svartika/ccnx,ebollens/ccnmp,svartika/ccnx,cawka/ndnx,cawka/ndnx,svartika/ccnx