perf script: Add stackcollapse.py script

Add stackcollapse.py script as an example of parsing call chains, and
also of using optparse to access command line options.

The flame graph tools include a set of scripts that parse output from
various tools (including "perf script"), remove the offsets in the
function and collapse each stack to a single line. The website also
says "perf report could have a report style [...] that output folded
stacks directly, obviating the need for stackcollapse-perf.pl", so here
it is.

This script is a Python rewrite of stackcollapse-perf.pl, using the perf
scripting interface to access the perf data directly from Python.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Brendan Gregg <bgregg@netflix.com>
Link: http://lkml.kernel.org/r/1460467573-22989-1-git-send-email-pbonzini@redhat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>