Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

bsdinstall: allow setting the root password via env variables

Reviewed by: 0mp, allanjude, asiciliano, dteske, pauamma, rpokala, sef
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D35588

bsdinstall: allow whitelabeling the scripts

Approved by: allanjude, asiciliano
Differential Revision: https://reviews.freebsd.org/D35197
Sponsored by: Rubicon Communications, LLC ("Netgate")

bsdinstall: inform users that typing will not be visible

Some users, especially those that are new, might be confused when passwd
does not echo anything. Inform users that the password will not be
visible.

PR: 196113
Submitted by: Byron Grobe <grobe0ba@gmail.com>

Remove trailing newline at EOF

MFC after: 3 days
X-MFC-to: stable/10

Make messages about typos appear on the screen instead of in the log file.

Reported by: lev
Approved by: re (kib)

Import bsdinstall. This is meant to be (eventually in conjunction with
pc-sysinstall) a replacement for sysinstall in the 9.0 release and beyond.
Currently supported platforms are sparc64, pc98, i386, amd64, powerpc, and
powerpc64. Integration into the build system will occur in the coming
weeks.

Merging with pc-sysinstall will use this code as a frontend, while
temporarily retaining the interactive partition editor here. This work
will be done in parallel with improvements on this code and release
integration.

Thanks to all who have provided testing and comments!