add conntrack_count and conntrack_max

[gregleroux]

Fixes #54

Summary of changes:

• add conntrack_count and conntrack
  /intel/psutil/netfilter/conntrackcount
  /intel/psutil/netfilter/conntrackmax

How to verify it:

• load task with this metrics:
  "/intel/psutil/net/netfilter/conntrackcount": {},
  "/intel/psutil/net/netfilter/conntrackmax": {},

Testing done:

A picture of a snapping turtle (not required but encouraged):

[snapbot]

Can one of the admins verify this patch?

[nanliu]

travis.ci VM does not appear to have /proc/sys/net/netfilter/

[kindermoumoute]

I received a response from Travis support, there is no plan to add /proc/sys/net/netfilter/ to travis.ci VM. The ultimate solution is to host manually those files in this repo, and copy it to /proc/sys/net/netfilter/ when running test (e.g. in an init() function).

[snapbot]

Can one of the admins verify this patch?

[snapbot]

Can one of the admins verify this patch?