test: writeaviddv50: replace 'type -P' with 'command -v' in test script
test: writeaviddv50: replace 'type -P' with 'command -v' in test script

type's option -P was not recognized on Ubuntu 12.04 and command is used
in the other regression test scripts

ebu/ebu-libmxf,Limecraft/ebu-libmxf,ebu/ebu-libmxf,stuarthicks/libmxf,Limecraft/ebu-libmxf,stuarthicks/libmxf,ebu/ebu-libmxf,stuarthicks/libmxf,stuarthicks/libmxf,Limecraft/ebu-libmxf,ebu/ebu-libmxf