perf/trace/scripting: rwtop script cleanup

A couple of fixes for the rwtop script:

- printing the totals and clearing the hashes in the signal handler
  eventually leads to various random and serious problems when running
  the rwtop script continuously.  Moving the print_totals() calls to
  the event handlers solves that problem, and the event handlers are
  invoked frequently enough that it doesn't affect the timeliness of
  the output.

- Fix nuisance 'use of uninitialized value' warnings

Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Message-Id: <1273466820-9330-4-git-send-email-tzanussi@gmail.com>
Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>