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 r257344,r257403:

Move /etc/keys to /usr/share/keys where users are less likely to modify them.

Approved by: bapt
Approved by: re (gjb)

Move /etc/keys to /usr/share/keys where users are less likely to modify them.

Requested by: secteam (cperciva, des)
Approved by: bapt

Add infrastructure for installing pkg(8) keys into /etc/keys/pkg and add
the current test key that packages will be signed with until 10.0-RELEASE.

Approved by: bapt
Discussed by: bapt with des
MFC after: 2 days