Do not remove local role file if given on the commandline

using this (for testing purpose):

    $ ansible-galaxy install COPYING
    - error: the file downloaded was not a tar.gz
    - COPYING was NOT installed successfully.
    - you can use --ignore-errors to skip failed roles.

this result in COPYING being erased, which is surprising for the user.
This also prevent erasing requirements.yml if someone use the wrong flag.