PersistReco does not support configuration of mixing reconstruction

In the tests test_hlt2_lines_reco_mix.qmt and test_hlt2_lines_reco_mix_full_mc.qmt, two instances of each line are run: one that takes reconstructed objects from the input file (produced by Brunel), and another that takes reconstructed objects from an on-the-fly reconstruction.

The current PersistReco configuration does not support this scheme. These tests are disabled in !685 (merged).