Move D-Bus policy file to /usr/share/dbus-1/system.d/

To better support stateless systems with an empty /etc, the old location
in /etc/dbus-1/system.d/ should only be used for local admin changes.
Package provided D-Bus policy files are supposed to be installed in
/usr/share/dbus-1/system.d/.

This is supported since dbus 1.9.18.

https://lists.freedesktop.org/archives/dbus/2015-July/016746.html
2 jobs for dbus-policy in 16 minutes and 40 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Build
passed #156150
fedora28_dist

00:07:56

 
  Test
passed #156151
fedora_from_dist

00:08:43