--ext option does not find external from LCG for platforms equivalent to but non released as LCG ones
The --ext option does not find external from LCG for platforms equivalent to but non released as LCG ones. In short:
$ lb-run --ext=ipython Gaudi/v32r2 which ipython
/cvmfs/lhcb.cern.ch/lib/lcg/releases/LCG_96b/ipython/5.8.0/x86_64-centos7-gcc8-opt/bin/ipython
but
$ lb-run -c best --ext=ipython Gaudi/v32r2 which ipython
WARNING:lb-run:Decided best platform to use is x86_64+avx2+fma-centos7-gcc8-opt
WARNING:lb-run:no LCG found: ignoring --ext option
/usr/bin/ipython