BUG: fix several problems in detection of GDAL version

- Move declaration of GDAL_CONFIG_CHECKING in otb-module-init.cmake to ensure gdal configuration in all cases (if statement)
- OTBCommon module needs to depend on OTBGDAL as GDAL module has to set OTB_USE_GDAL_20 before configuring otbConfigure.h
- Set mode to STATUS for GDAL version >= to 2.0

All these issues were found compiling gdal trunk (2.1.0dev) with clang 3.5.