Add support for multi-year CICE boundary files in python tool

[jostbr]

When running with open boundary conditions in CICE and the run includes a transition from one year to another, the model expects one boundary file for each year. Need to add support for such multi-year boundary file generation in tools/cice_bry.py. Currently only a boundary file within one year is supported. I (Jostein) will do this and then close this issue.