run handlers in conda environment

Since some lhcbpr nodes (e.g. lblhcpr6.cern.ch) do not have a connection to the network outside CERN, the idea is to produce the environment (using conda-pack) for handlers centrally by the jenkins job (e.g. once a day) and push it eos (see: nightlies-jenkins-scripts!24 (merged)). It may be also advantageous because of setup time - it takes several minutes to set that conda environment, so doing it repeatedly for each test is not optimal in terms of resources.