mpi_grid_dims seems to be ignored

[gsavva]

Executing hp.x from q-e-sirius via the command:
mpirun -np 4 hp.x --control.mpi_grid_dims=1:4 -i hp.in > hp.out
ignores the dimensions given and instead sets MPI grid to [2 2] since 4 is a square number (relevant code in q-e-sirius)

The same occurs when mpi_grid_dims is set via a config.json file as:
mpirun -np 4 hp.x -sirius_cfg sirius.json -i hp.in > hp.out
with the contents of sirius.json as below:

{
  "control": {
    "mpi_grid_dims": [1,4]
  }
}

In fact, even if the content of the config.json is completely wrong, for example "mpi_grid_dims": [1,4,3] (wrong dimensions), no errors are thrown.