InDetRIO_OnTrack: Fix TrkEventAthenaPoolTest failures.

InDetRIO_OnTrack:

Starting from nightly 2020-07-10T2136 (so yesterday' one/ latest wrt the time of this MR obviously)

Failures have been observed in e.g http://atlas-computing.web.cern.ch/atlas-computing/links/distDirectory/gitwww/MASTERWebArea/ardoc_web_areamaster64BC7G8AthenaOpt/ARDOC_TestLog_2020-07-10T2136/Tracking_TrkEventCnv_TrkEventAthenaPool___TrkEventAthenaPoolConf__TrkEventAthenaPoolTest__m.html

• Fixes for TrkEventAthenaPoolTest failures.
• Make clear which is the P->T constructor and that the object in this context is completed by setValues
• In short one of the ctors is a bit special , used in P->T, and the cnv runs the setValues to complete the object.
• This MR add comments to these ctors, and move the filling of variables related to e.g detectorElement info inside the setValues in case these ctor is used.

After the changes in the MR I see (e.g test succeeds)

Test project /scratch/anastopoulos/Athena-git/build
      Start  1: InDetEventTPCnv_SiWidthCnv_p1_test_ctest
 1/24 Test  #1: InDetEventTPCnv_SiWidthCnv_p1_test_ctest .........................   Passed    1.58 sec
      Start  2: InDetEventTPCnv_SiWidthCnv_p2_test_ctest
 2/24 Test  #2: InDetEventTPCnv_SiWidthCnv_p2_test_ctest .........................   Passed    1.47 sec
      Start  3: InDetEventTPCnv_PixelClusterCnv_p1_test_ctest
 3/24 Test  #3: InDetEventTPCnv_PixelClusterCnv_p1_test_ctest ....................   Passed    1.29 sec
      Start  4: InDetEventTPCnv_PixelClusterCnv_p2_test_ctest
 4/24 Test  #4: InDetEventTPCnv_PixelClusterCnv_p2_test_ctest ....................   Passed    1.24 sec
      Start  5: InDetEventTPCnv_PixelClusterCnv_p3_test_ctest
 5/24 Test  #5: InDetEventTPCnv_PixelClusterCnv_p3_test_ctest ....................   Passed    1.48 sec
      Start  6: InDetEventTPCnv_PixelClusterContainerCnv_p1_test_ctest
 6/24 Test  #6: InDetEventTPCnv_PixelClusterContainerCnv_p1_test_ctest ...........   Passed    1.78 sec
      Start  7: InDetEventTPCnv_PixelClusterContainerCnv_p2_test_ctest
 7/24 Test  #7: InDetEventTPCnv_PixelClusterContainerCnv_p2_test_ctest ...........   Passed    1.39 sec
      Start  8: InDetEventTPCnv_PixelClusterContainerCnv_p3_test_ctest
 8/24 Test  #8: InDetEventTPCnv_PixelClusterContainerCnv_p3_test_ctest ...........   Passed    1.47 sec
      Start  9: InDetEventTPCnv_SCT_ClusterContainerCnv_p2_test_ctest
 9/24 Test  #9: InDetEventTPCnv_SCT_ClusterContainerCnv_p2_test_ctest ............   Passed    1.62 sec
      Start 10: InDetEventTPCnv_SCT_ClusterContainerCnv_p3_test_ctest
10/24 Test #10: InDetEventTPCnv_SCT_ClusterContainerCnv_p3_test_ctest ............   Passed    1.42 sec
      Start 11: InDetEventTPCnv_TRT_DriftCircleContainerCnv_p2_test_ctest
11/24 Test #11: InDetEventTPCnv_TRT_DriftCircleContainerCnv_p2_test_ctest ........   Passed    1.66 sec
      Start 12: InDetEventTPCnv_SCT_ClusterCnv_p1_test_ctest
12/24 Test #12: InDetEventTPCnv_SCT_ClusterCnv_p1_test_ctest .....................   Passed    1.32 sec
      Start 13: InDetEventTPCnv_SCT_ClusterCnv_p2_test_ctest
13/24 Test #13: InDetEventTPCnv_SCT_ClusterCnv_p2_test_ctest .....................   Passed    1.62 sec
      Start 14: InDetEventTPCnv_SCT_ClusterCnv_p3_test_ctest
14/24 Test #14: InDetEventTPCnv_SCT_ClusterCnv_p3_test_ctest .....................   Passed    1.44 sec
      Start 15: InDetEventTPCnv_TRT_DriftCircleCnv_p1_test_ctest
15/24 Test #15: InDetEventTPCnv_TRT_DriftCircleCnv_p1_test_ctest .................   Passed    1.32 sec
      Start 16: InDetEventTPCnv_TRT_DriftCircleCnv_p2_test_ctest
16/24 Test #16: InDetEventTPCnv_TRT_DriftCircleCnv_p2_test_ctest .................   Passed    1.44 sec
      Start 17: InDetEventTPCnv_PixelGangedClusterAmbiguitiesCnv_p1_test_ctest
17/24 Test #17: InDetEventTPCnv_PixelGangedClusterAmbiguitiesCnv_p1_test_ctest ...   Passed    1.73 sec
      Start 18: InDetEventTPCnv_InDetLowBetaCandidateCnv_p1_test_ctest
18/24 Test #18: InDetEventTPCnv_InDetLowBetaCandidateCnv_p1_test_ctest ...........   Passed    1.47 sec
      Start 19: TrkEventAthenaPool_TrkEventTPCnv_14.5.0_ctest
19/24 Test #19: TrkEventAthenaPool_TrkEventTPCnv_14.5.0_ctest ....................   Passed   90.58 sec
      Start 20: TrkEventAthenaPool_TrkEventTPCnv_15.6.7_ctest
20/24 Test #20: TrkEventAthenaPool_TrkEventTPCnv_15.6.7_ctest ....................   Passed   95.81 sec
      Start 21: TrkEventAthenaPool_TrkEventTPCnv_16.6.2.1_ctest
21/24 Test #21: TrkEventAthenaPool_TrkEventTPCnv_16.6.2.1_ctest ..................   Passed  102.32 sec
      Start 22: TrkEventAthenaPool_TrkEventTPCnv_17.2.8_ctest
22/24 Test #22: TrkEventAthenaPool_TrkEventTPCnv_17.2.8_ctest ....................   Passed   96.86 sec
      Start 23: TrkEventAthenaPool_TrkEventTPCnv_18.0.0_ctest
23/24 Test #23: TrkEventAthenaPool_TrkEventTPCnv_18.0.0_ctest ....................   Passed   89.62 sec
      Start 24: TrkEventAthenaPool_TrkEventTPCnv_20.1.7.2_ctest
24/24 Test #24: TrkEventAthenaPool_TrkEventTPCnv_20.1.7.2_ctest ..................   Passed  137.97 sec

Mentioning @oda and @ssnyder that might be interested, have observed this behaviour, or have comments?

PS : Perhaps for another MR, but perhaps this ctor should be made also private or the setValues public? Now is a mixture of public/private and Cnv friendship from what I can tell. But needs a bit of care I guess, so tried to leave this out for now. I guess there is a way to indicate even better that this ctor and the setValues work together in a specific way in the context of Cnv?