DB download verification error

[Matthias]

When downloading reference with:

`iphop download --db_dir db/ --db_version iPHoP_db_Aug23_rw --full_verify --no_prompt`

this fails with:

Job in error state.. tool_id: iphop_build_database, exit_code: 1, stderr: Traceback (most recent call last):
  File "/home/berntm/miniconda3/envs/__iphop@1.3.3/bin/iphop", line 10, in <module>
    sys.exit(cli())
  File "/home/berntm/miniconda3/envs/__iphop@1.3.3/lib/python3.8/site-packages/iphop/iphop.py", line 128, in cli
    args["func"](args)
  File "/home/berntm/miniconda3/envs/__iphop@1.3.3/lib/python3.8/site-packages/iphop/modules/master_downloader.py", line 35, in main
    full_verify(args["db_dir"],logger)
  File "/home/berntm/miniconda3/envs/__iphop@1.3.3/lib/python3.8/site-packages/iphop/modules/master_downloader.py", line 171, in full_verify
    with open(file_list_file, "r", newline='') as f:
FileNotFoundError: [Errno 2] No such file or directory: 'db/md5checkfile.txt'

Workaround is to download without --full_verify

[Simon Roux]

Thanks for reporting this. This is expected, just an unclear documentation I think: the “--full_verify” argument is only meant to be used when the database has been downloaded and extracted to verify if it is complete. But if no database has been downloaded yet, it will fail as you see here. I’ll look into modifying the code and/or doc to make it more clear.

[Simon Roux]

Readme updated