Add const to methods of MdtCalibrationTool to fix const-correctness issues

Add const to methods of MdtCalibrationTool to fix const-correctness issues of MdtDriftCircleOnTrackCreator of MuonCalibPatRec.

http://atlas-computing.web.cern.ch/atlas-computing/links/distDirectory/gitwww/experimentalWebArea/nicos_web_areaconstmaster_Athena_x86_64centos7gcc8opt64BC7G8AthenaOpt/NICOS_Log_2019-06-08T1008/MuonSpectrometer_MuonReconstruction_MuonRIO_OnTrackCreators_MdtDriftCircleOnTrackCreator.html

http://atlas-computing.web.cern.ch/atlas-computing/links/distDirectory/gitwww/experimentalWebArea/nicos_web_areaconstmaster_Athena_x86_64centos7gcc8opt64BC7G8AthenaOpt/NICOS_Log_2019-06-08T1008/MuonSpectrometer_MuonCalib_MuonCalibPatRec.html

+ MuonSpectrometer/MuonReconstruction/MuonRIO_OnTrackCreators/MdtDriftCircleOnTrackCreator
+ MuonSpectrometer/MuonCalib/MdtCalib/MdtCalibSvc

were compiled by

cmake -DATLAS_PACKAGE_FILTER_FILE=../package_filters.txt  -DATLAS_ALLOW_TOOLHANDLE_NONCONSTNESS=OFF ../athena/Projects/WorkDir
make