1. the disk io statistic data as: nread, nwritten, reads, writes, rtime, wtime;
2. the free memory under global zone;
3. the net io statistic data as: rbytes64, ipackets64, idrops64, ierrors, obytes64, opackets64, odrops64, oerrors.
The new feature branch adds the above missing statistic data based on the psutil project (https://psutil.readthedocs.io/), it has been tested under solaris ( Oracle Solaris 11.4 X86) and illumos (OmniOS v11 r151044).
This commit adds support for VirtualMemory() in package mem. The support
only extends to total memory capcity, since that is all that is required
in Nomad. It does take into account global versus non-global zones, and
does not use cgo.
This has been tested inside a zone in the Joyent public cloud for a
non-global zone, and in the global zone of a SmartOS virtual machine.