Adds systime to nmea file.

measurement_main.py

             nmea_sentence = ser.readline()  # GPRMC
             nmea_str = nmea_sentence.decode("utf-8")
             if nmea_str.startswith("$GPRMC"):
-                write_to_file(output_file, nmea_str)
+                time_epoch = subprocess.check_output(CMD_TIME_EPOCH, shell=True).decode(
+                    "utf-8"
+                )
+                write_to_file(output_file, "{},{}".format(nmea_str, time_epoch))
     except:
         if not ser.is_open:
             print_message("GPS serial port is closed. Exit monitoring thread.")
                 sleep(2)
                 modem_serial_obj.write(b'at+cfun=1\r\n')
                 sleep(NR_SERIAL_RESPOND_TIME)
-                sleep(2)
-                os.system("/root/connect-modem.py -s")
-                sleep(5)
-                os.system("/root/connect-modem.py -l {}".format(provider))
         except Exception as e:
             if not modem_serial_obj.is_open:
                 print_message("Serial port is closed. {}".format(e))
                     "Something went wrong while writing to serial. {}".format(e)
                 )
                 os.system("/root/connect-modem.py -s")
+        sleep(2)
+        os.system("/root/connect-modem.py -s")
+        sleep(5)
+        os.system("/root/connect-modem.py -l {}".format(provider))
     else:
         os.system("/root/connect-modem.py -s")
         sleep(5)