cachstat separation between read and writes doesn't make much sense. During tests
its seen that a workload that is supposed to be completely in the missed category
appears to be 50% hit.

This patch rewrites the BCC tool to be more inline with Brendan Gregg's original
cachestat perf tool which makes more sense:
https://github.com/brendangregg/perf-tools/blob/master/fs/cachestat
http://www.brendangregg.com/blog/2014-12-31/linux-page-cache-hit-ratio.html

Fixes Issue: #1586
Signed-off-by: Joel Fernandes <joelaf@google.com>