perf test: Use machine__new_host in dwarf unwind test

This is more straightforward than what we have now.

It also fixes a segfault within machine__exit, that's caused by not
creating kernel maps for machine.. We're calling
machine__destroy_kernel_maps in machine__exit since commit:

  ebe9729c perf machine: Fix to destroy kernel maps when machine exits
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1449131658-1841-2-git-send-email-jolsa@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/dwarf-unwind.c

@@ -160,14 +160,11 @@ static int krava_1(struct thread *thread)
 
 int test__dwarf_unwind(int subtest __maybe_unused)
 {
-	struct machines machines;
 	struct machine *machine;
 	struct thread *thread;
 	int err = -1;
 
-	machines__init(&machines);
-
-	machine = machines__find(&machines, HOST_KERNEL_ID);
+	machine = machine__new_host();
 	if (!machine) {
 		pr_err("Could not get machine\n");
 		return -1;
@@ -199,7 +196,6 @@ int test__dwarf_unwind(int subtest __maybe_unused)
 
  out:
 	machine__delete_threads(machine);
-	machine__exit(machine);
-	machines__exit(&machines);
+	machine__delete(machine);
 	return err;
 }