perf tests: Check python path on attr and binding test

Current perf test code tries to execute python version 2 in order to
test attributes on perf_event_open syscall.  However it's not default
python version anymore a system can have python v3 only or v2 with a
different name (e.g. python2).  So if there's no such python interpreter
with the name 'python', the test would fail like this (yes, it's
happened on my new archlinux laptop :).

13: struct perf_event_attr setup                 🇸🇭

 python: command not found
 FAILED!

As we can pass name of the python interpreter on make, use it for
the attr test also.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1355729101-31317-1-git-send-email-namhyung@kernel.org


[ committer note: Added the same mechanism to the python binding test ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>