Install netcat everywhere

Summary:
Twice this evening, nc was installed on a server
to perform the following connectivity tests:

• on Equatower, connect to Ysul Salt master
• on Dwellers, connect to Equatower registry

It seems nc is probably a good idea on each server.

Test Plan: nc

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D2002