WS-179: subtask #6 -- remove argparse namespace dependencies in classes

This addresses https://open-jira.nrao.edu/browse/WS-184.

• args are accessed only in locations_report.init()
• directory/file-related errors throw custom exception

apps/cli/executables/datafetcher/datafetcher/utilities.py

@@ -27,6 +27,7 @@ from .errors import (
     NGASServiceErrorException,
     SizeMismatchException,
     TERMINAL_ERROR_CODES,
+    FileErrorException,
 )
 
 LOG_FORMAT = "%(module)s.%(funcName)s, %(lineno)d: %(message)s"
@@ -363,7 +364,7 @@ def confirm_complete_args(args: List[str]):
         # did they just forget to specify it?
         if output_dir_arg.startswith("--"):
             raise MissingSettingsException("--output-dir is required")
-        raise FileNotFoundError(f"output dir '{output_dir_arg}' not found")
+        raise FileErrorException(f"output dir '{output_dir_arg}' not found")
     if not path_is_accessible(output_dir):
         raise FileNotFoundError(f"permission denied on {output_dir}")