aviary convert_engine needs better error message when input deck file does not exist

[hschilling]

Description

When running the aviary convert_engine command, if the input file does not exist, the error message is not a clear indication of what the problem is

  File "/Users/hschilli/Documents/OpenMDAO/dev/IA884-cmd-line-refactor/aviary/utils/conversion_utils.py", line 25, in _strparse
    yield typ(sub)
          ^^^^^^^^
ValueError: invalid literal for int() with base 10: '# cre'

Should explicitly say the file does not exist.

Example

aviary convert_engine turbofan_23k_1.eng turbofan_23k_1.csv -f GASP

Aviary Version

0.10.0.dev0

Relevant environment information

No response