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

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