ipa: check if provided config file exists
Add a parser check to verify config file supplied to the ipa
command exists. Previously, invalid file paths would not results
in any error and would just silently proceed with default config.
https://fedorahosted.org/freeipa/ticket/6114
Reviewed-By: Petr Spacek <pspacek@redhat.com>
Reviewed-By: Martin Basti <mbasti@redhat.com>