bsdinstall: Add quotes around error message argument

[thj]

Summary

bsdinstall: Add quotes around error message argument

When error is called with a message with spaces (and probably multiple lines)
these are passed into dialog unquoted and an error message is presented in the
form:

"Expected no more than 3 tokens for --msgbox have 9"

This has been seen on recent snapshots which also suffer from https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=261272

Test Plan

The following script shows the bug and the fix

	#!/bin/sh

	error()                                                                       
	{                                                                             
		dialog --backtitle "FreeBSD Installer" --title "Error" --msgbox $1 0 0
	}                                                                             

	error_fixed()                                                                       
	{                                                                             
		dialog --backtitle "FreeBSD Installer" --title "Error" --msgbox "$1" 0 0
	}                                                                             

	error "bug not fixed"
	read tmp
	error_fixed "bug fixed"

[allanjude]

yeah, --msgbox complains "Expected no more than 3 tokens for --msgbox, have 9." or however many words there were in your error message, plus the "0 0" parameters.

It seems we just didn't encounter this very often previously.

[koobs]

Did this end up being EN'd for currently supported RELEASE's ?

We've been seeing increasing reports of this issue for people customising the distribution list or similar