iostat.py: add statistic metric await.

Signed-off-by: Vasiliy Kiryanov <vasiliy.kiryanov@gmail.com>
iostat.py: add statistic metric util.

Signed-off-by: Vasiliy Kiryanov <vasiliy.kiryanov@gmail.com>
Add g1gc collector

G1 GC collector:
    script that scan G1 GC log and populate OpenTSDBmetrics into stdout