perf build: Test correct path of perf in build-test

perf build: Test correct path of perf in build-test

If an 'O' is passed to 'make build-test', many 'test -x' and 'test -f'
will fail because perf resides in a different directory. Fix this by
computing PERF_OUT according to 'O' and test correct output files.
For make_kernelsrc and make_kernelsrc_tools, set KBUILD_OUTPUT_DIR
instead because the path is different from others ($(O)/perf vs
 $(O)/tools/perf).

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1452830421-77757-4-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>