Use subprocess instead of pty

Much simpler and more robust. This should also ease submitting the
script to a batch scheduler. And we can now check the return code of
Matlab.

Convert_Matlab/inst_eddies_v6.py

@@ -16,9 +16,9 @@ import scipy.io as sio
 import datetime
 import f90nml
 import sys
-import pty
 import os
 from dateutil import parser
+import subprocess
 
 def define_fields(writers):
     """writers is a dictionary of shapefile.Writer objects."""
@@ -145,7 +145,7 @@ while True:
     if os.access(adt_file, os.R_OK):
         print("Processing", my_date, "...")
         os.symlink(adt_file, "adt.mat")
-        pty.spawn(["matlab", "-batch", "inst_eddies"])
+        subprocess.run(["matlab", "-batch", "inst_eddies"], check = True)
         matlab_data = sio.loadmat("adt_v6.mat", squeeze_me = True,
                                   variable_names = ("date_num", "X", "Y",
                                                     "Anticyclonic_Cell",