run_telfile.py alter in order to alter only what is expected

If running run_telfile.py script with positional argument 'alter', this script may alter other information than the one expected:

• e.g. for a 2D result file, nplan would be changed to at least 1 (see I think method nplan in telemac_file.py: self._nplan = max(1, self.get_mesh_nplan())),
• original ipobo array is not copied in altered file (even if present in the original file) but default values (of 0?) are. In order to keep ipobo array, giving the boundary condition file with option -b seems to be currently needed (by default in telemac_file.py, it seems that ipob arrays are filled with 0 values).

The nplan issue was discussed in #957 (closed)