xci: kubespray: Fix inventory when configuring keys on targethosts

xci: kubespray: Fix inventory when configuring keys on targethosts

The SSH keys for the OPNFV host have been configured in the
configure-opnfvhost.yml playbook so we shouldn't do that in a playbook
that is only meant to configure the target hosts. As such, fix the group
to use 'k8s-cluster' instead.

Since the targethosts playbook does not apply to all hosts anymore, we
can simply drop the list of required packages and only install 'netaddr'
on the OPNFV host which is the host that needs it. Similarly, the dbus
package is only needed on the targethosts.

Change-Id: I293ad83a3a95797d9025f2cddd7849be7b3a49da
Signed-off-by: Markos Chandras <mchandras@suse.de>