FastJet Updates, master branch (2020.03.06.)

Triggered by athena!30643 (merged), synchronised the FastJet build setup between the "LCG based" projects.

While using LCG_96<X>, we need to build FastJet ourselves in any Athena based project that wants thread-safety. But FastJetContrib we should pick up from the LCG release, to make it possible to use packages from LCG that depend on FastJetContrib. (Cough... Rivet, cough...)

AE Build SUCCESS
Build logfiles are available at Jenkins [AE-MERGE-REQUEST-CC7 #206]

mentioned in commit 2a053c2a

merged

Thanks @akraszna!