[rootcp] Write out keys only if cycle number increases
[rootcp] Write out keys only if cycle number increases

Fixes https://sft.its.cern.ch/jira/browse/ROOT-8528.

olifre/root,olifre/root,karies/root,root-mirror/root,olifre/root,olifre/root,olifre/root,olifre/root,karies/root,root-mirror/root,root-mirror/root,olifre/root,root-mirror/root,karies/root,root-mirror/root,root-mirror/root,karies/root,root-mirror/root,karies/root,root-mirror/root,karies/root,root-mirror/root,olifre/root,olifre/root,olifre/root,root-mirror/root,karies/root,karies/root,root-mirror/root,olifre/root,karies/root,karies/root,karies/root