oeqa/runtime/dnf: use dnf-test packages

oeqa/runtime/dnf: use dnf-test packages

Instead of installing run-postinsts with it's postinst scripts causing
systemd restarts, use the new dnf-test-* packages instead.

Remove from the installroot tests entirely as they're exercised enough
using just busybox.

Rewrite the exclude test to be simplier now these packages are not going
to be part of an existing dependency chain.

[ YOCTO #14787 ]

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>