Make LBN histogram names more ROOT friendly

Tomasz Boldrequested to merge
tbold/athena:fix-lbn-histograms into master

This MR is a tiny fix/change to the histograms naming convention for LBN based hists. Tagging @onyisi and @cburton @fwinkl Addresses: https://its.cern.ch/jira/browse/ATLASDQ-780

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