Enhance node-status to show custom columns

[shantanugadgil]

As discussed in
#3684

... request you to consider this as a feature request to enhance the node-status command to
choose which columns to show.

The easiest way comes to mind is a '-o' flag like the 'ps' command or the LVM2 command lines
pvs, vgs, lvs.

Nomad version

Output from nomad version
0.7.1

Operating system and Environment details

CentOS 7/Ubuntu 14.04/Ubuntu 16.04

Regards,
Shantanu

[lgfa29]

Closing this in favour of #15894. While not exactly the same it would be best to standardize our commands around common flags, such as -json and -t. Thanks for porposal @shantanugadgil!