trace: move setting of group name into Makefiles

trace: move setting of group name into Makefiles

Having tracetool.py figure out the right group name from just
the input filename is not practical when considering the
different build vs src path combinations. Instead simply take
the group name as a command line arg from the Makefile, which
can trivially provide the right name.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-id: 20170125161417.31949-6-berrange@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>