Added cached variables for SRCS_REPOSITORY and GEANT4_TAG

Added cached variables for SRCS_REPOSITORY and GEANT4_TAG

As requested during the meeting.

Fixes LHCBGAUSS-590

Merge branch 'LBCORE-1009' of ssh://gitlab.cern.ch:7999/bcouturi/Geant4

* 'LBCORE-1009' of ssh://gitlab.cern.ch:7999/bcouturi/Geant4:
  Added cached variables for SRCS_REPOSITORY and GEANT4_TAG

See merge request !3


git-svn-id: svn+ssh://svn.cern.ch/reps/lhcb/Geant4/trunk@199081 4525493e-7705-40b1-a816-d608a930855b