SofaTest: make initialisation of PluginRepository more robust
SofaTest: make initialisation of PluginRepository more robust

Using Utils::getExecutableDirectory() allow for a subdirectory in bin,
like bin/Release.


Former-commit-id: 7b6944e37acd1f0dd86c7df6a9cc276c83d5c10a
FabienPean/sofa,FabienPean/sofa,hdeling/sofa,FabienPean/sofa,hdeling/sofa,hdeling/sofa,Anatoscope/sofa,hdeling/sofa,FabienPean/sofa,Anatoscope/sofa,hdeling/sofa,hdeling/sofa,FabienPean/sofa,FabienPean/sofa,Anatoscope/sofa,hdeling/sofa,Anatoscope/sofa,hdeling/sofa,FabienPean/sofa,FabienPean/sofa,Anatoscope/sofa,FabienPean/sofa,Anatoscope/sofa,Anatoscope/sofa,FabienPean/sofa,Anatoscope/sofa,hdeling/sofa,hdeling/sofa,Anatoscope/sofa