perf test: Use machine__new_host in dwarf unwind test

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:

  ebe9729c8c31 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.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>