support perf counters on sched_switch

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
sched_switch can return a dict of what changed during the scheduling period (useful for perf counters)

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
Perf-info: track perf PMU counter changes per-tid and output in text,json,mongodb

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
make sure we only look for perf_ in the stream event context to avoid clashes with event fields

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>