tools lib traceevent: Implement new API tep_get_ref()

This patch implements a new API of the tracevent library:

  int tep_get_ref(struct tep_handle *tep);

The API returns the reference counter "ref_count" of the tep handler.
As "struct tep_handle" is internal only, its members cannot be accessed
by the library users, the API is used to get the reference counter.

Signed-off-by: Tzvetomir Stoyanov <tstoyanov@vmware.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/20181130154646.890615385@goodmis.org


Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>