AccumulatorCache: make cache statistics global and add time

Make the cache hit/miss statistics of AccumulatorCache available globally and also measure the time for each execution. Add printStats() to print summary.

Also cleanup unit test definition.

Example output from LS2_v1_newJO test (partial and after some local fixes to be submitted soon):

----------------------------------------------------------------------------------------------------------
AccumulatorCache                                                       |    Hits (time) |  Misses (time) |
----------------------------------------------------------------------------------------------------------
TriggerMenuMT.HLTMenuConfig.Muon.generateMuon._muEFCBStepSeq           |      1 ( 0.0s) |      5 (38.0s) |
TriggerMenuMT.HLTMenuConfig.Muon.generateMuon._muEFSAStepSeq           |      5 ( 0.2s) |      5 (32.7s) |
IOVDbSvc.IOVDbSvcConfig.IOVDbSvcCfg                                    |  41142 (15.6s) |     79 ( 0.2s) |
...ndAlg.AtlasTrackingGeometryCondAlgConfig.TrackingGeometryCondAlgCfg |   2811 ( 6.6s) |     51 ( 4.0s) |
TrkConfig.AtlasTrackSummaryToolConfig.AtlasTrackSummaryToolCfg         |    115 ( 0.6s) |     15 ( 3.4s) |
TriggerMenuMT.HLTMenuConfig.Electron.generateElectron._ftfSeq          |      4 ( 0.0s) |      3 ( 2.7s) |
TriggerMenuMT.HLTMenuConfig.Jet.JetTrackingConfig.JetTrackingCfg       |      4 ( 0.0s) |      3 ( 2.7s) |
TriggerMenuMT.HLTMenuConfig.Muon.generateMuon._muCombStepSeq           |      2 ( 0.0s) |      3 ( 2.4s) |
TriggerMenuMT.HLTMenuConfig.Muon.generateMuon.decodeCfg                |      1 ( 0.0s) |      7 ( 1.8s) |
TriggerMenuMT.HLTMenuConfig.Muon.generateMuon._muFastStepSeq           |      6 ( 0.0s) |      3 ( 1.3s) |
...enuMT.HLTMenuConfig.Electron.generateElectron._precisionTrackingSeq |      5 ( 0.0s) |      2 ( 1.2s) |
TriggerMenuMT.HLTMenuConfig.Muon.generateMuon._muEFIsoStepSeq          |      0 ( 0.0s) |      1 ( 0.8s) |
TriggerMenuMT.HLTMenuConfig.Electron.generateElectron._fastCaloSeq     |      4 ( 0.0s) |      3 ( 0.7s) |
TrigT2CaloCommon.TrigCaloDataAccessConfig.trigCaloDataAccessSvcCfg     |     12 ( 0.0s) |      8 ( 0.7s) |

cc @tbold @ktopolni @smh @rbielski