Extend VNC port range

Extend VNC port range

Per the attached bug, if a large number of instances are colocated
on a single compute node it is possible to exhaust the allowed VNC
ports.  This change extends the range to include 1024 ports, which
with the default 16x overcommit ratio in Nova means we could handle
a fully loaded 64 core server.  That's _probably_ overkill, but I
think it makes sense to overshoot a bit on this and ensure nobody
runs into weird problems because their VNC ports weren't allowed
through the firewall.

Change-Id: Ia48602e82b8e0fbb585371ea514eea3c2334dab0
Closes-Bug: 1678025