Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC: r256770,r257142,r257145,r257146,r257147,r257148,
r257149,r257150,r257158,r257159,r257164,r257168,
r257193

- Support checking signature for pkg bootstrap from remote
and for 'pkg add ./pkg.txz'

- Be verbose on where pkg is being bootstrapped from.

- Add support for reading configuration files from /etc/pkg.
For now only /etc/pkg/FreeBSD.conf is supported.

- Add test package signing key fingerprint into /etc/keys/pkg/trusted.

- Disable fingerprint checking by default for now as the official
packages are not yet signed.

Approved by: bapt
Approved by: re (glebius)

Add support for reading configuration files from /etc/pkg.
For now only /etc/pkg/FreeBSD.conf is supported. Its style is:

Repo: {
URL: "...",
MIRROR_TYPE: "...",
...
}

The configuration will be read from /usr/local/etc/pkg.conf if exists,
otherwise /etc/pkg/FreeBSD.conf

Approved by: bapt
MFC after: 2 days