fix bugs in main.cpp of navier-stokes solver
fix bugs in main.cpp of navier-stokes solver

- the file path to the target restarting file.
- forgot to implement writing restarting data
- remove the use of finalize(). It currently conflict with
  PetscFinalize() somehow.

mesnardo/PetIBM,barbagroup/PetIBM,piyueh/PetIBM,mesnardo/PetIBM,mesnardo/PetIBM