Move D-Bus conf file to $(datadir)/dbus-1/system.d

Since D-Bus 1.9.18 configuration files installed by third-party should
go in $(datadir)/dbus-1/system.d.  The old location is for sysadmin
overrides.  Also check that we have recent enough D-Bus to use the new
location.

https://lists.freedesktop.org/archives/dbus/2015-July/016746.html
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passed #465327
build-fedora

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