Testing: Use fixed width integer types instead of natural types

testing/adios2/bindings/c/SmallTestData_c.h

testing/adios2/bindings/c/TestBPWriteTypes.c

testing/adios2/bindings/c/TestBPWriteTypes_nompi.c

testing/adios2/engine/SmallTestData.h

testing/adios2/engine/adios1/TestADIOS1WriteRead.cpp

testing/adios2/engine/bp/TestBPWriteProfilingJSON.cpp

testing/adios2/engine/bp/TestBPWriteRead.cpp

testing/adios2/engine/bp/TestBPWriteReadfstream.cpp

testing/adios2/engine/bp/TestBPWriteReadstdio.cpp

testing/adios2/engine/hdf5/TestHDF5WriteRead.cpp

testing/adios2/interface/TestADIOSInterfaceWrite.cpp