change how restart file is specified

[nmizukami]

Here is how restart file setup works after this PR.

1. get fname_state_in
2. if fname_state_in in control file is 'STATE_IN_NC' AND cesm/ctsm run type is branch or hybrid, construct restart file based on RUN_REFCASE and RUN_REFDATE, RUN_REFTOD and set the constructed name to fname_state_in.
3. if fname_state_in in control file is 'STATE_IN_NC' only, set "empty" to fname_state_in. (so cold start)
4. neither 2 nor 3 == something other than "empty", trust user put a valid restart file name in control file. if not, mizuRoute will complains.

resolve #621