MFC: r328695,r328720,r328784,r328795 share/examples/bhyve/vmrun.sh additions
and cleanups

r328695:
Add option '-n' network device emulation type which has a default
of virtio-net
PR: 225558
Submitted by: Johannes Lundberg <johalun0@gmail.com>

r328720:
Add -n <network device emulation type> to usage synopsis
forgotten in r328695.

Fix long lines in usage.
Consistently use "default:" rather than "default is"

r328784:
Clean up long lines.

r328795:
Fold constants and unify vnc variable names.

Approved by: grehan (mentor)

PR: 225558