perf scripts python: Add Python 3 support to sched-migration.py

perf scripts python: Add Python 3 support to sched-migration.py

Support both Python 2 and Python 3 in the sched-migration.py script.
This should have no functional change.

Signed-off-by: Jeremy Cline <jeremy@jcline.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Herton Krzesinski <herton@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/0100016341a737a5-44ec436f-3440-4cac-a03f-ddfa589bf308-000000@email.amazonses.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>