test_make_nitf.py uses show_nitf instead of show_nitf++

[kjurka]

Trying to run the python sample test_make_nitf.py errors:

ERROR: test_make_image_nitf (__main__.TestCreator)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "test_make_nitf.py", line 89, in test_make_image_nitf
    self.make_image_nitf()
  File "test_make_nitf.py", line 205, in make_image_nitf
    subprocess.run(['show_nitf', outfile])
  File "/usr/local/anaconda3-2019.10-tf2/lib/python3.7/subprocess.py", line 472, in run
    with Popen(*popenargs, **kwargs) as process:
  File "/usr/local/anaconda3-2019.10-tf2/lib/python3.7/subprocess.py", line 775, in __init__
    restore_signals, start_new_session)
  File "/usr/local/anaconda3-2019.10-tf2/lib/python3.7/subprocess.py", line 1522, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: 'show_nitf': 'show_nitf'

Changing this to show_nitf++ runs without issue.