flow: implement reduce for Nodes step
flow: implement reduce for Nodes step

Change-Id: Idba26ce3b0adcda91a185470ffb567eef00dfa81
Reviewed-on: https://softwarefactory-project.io/r/5651
Reviewed-by: Sylvain Baubeau <b0a7dc08a3f38d713e107103b0a85b0badc14b84@redhat.com>
Tested-by: Sylvain Baubeau <b0a7dc08a3f38d713e107103b0a85b0badc14b84@redhat.com>
Workflow: Sylvain Baubeau <b0a7dc08a3f38d713e107103b0a85b0badc14b84@redhat.com>

lebauce/skydive,redhat-cip/skydive,lebauce/skydive,skydive-project/skydive,safchain/skydive,lebauce/skydive,safchain/skydive,lebauce/skydive,skydive-project/skydive,skydive-project/skydive,safchain/skydive,safchain/skydive,skydive-project/skydive,safchain/skydive,lebauce/skydive,safchain/skydive,redhat-cip/skydive,lebauce/skydive,skydive-project/skydive,safchain/skydive,skydive-project/skydive,skydive-project/skydive,redhat-cip/skydive,safchain/skydive,lebauce/skydive,lebauce/skydive