perf tools: Allow shuffling the build tests

perf tools: Allow shuffling the build tests

Those tests take a long time and sometimes we stop it, so allow randomly
shuffling the tests so that we have a better chance of running more of
them in partial 'make build-test' runs.

Using it just on the 'build-test' target, i.e.:

   make -C tools/perf build-test

Is equivalent to:

   make SHUF=1 -C tools/perf -f tests/make

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-ey7461i9q4k8u0987j8guun6@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>