Mail handler behavior on complete/incomplete attachment processed

When creating or comment an issue via mail handler:

1. Attachments have been successfully processed it prints to the log

   Problem: The issue was created but the email was not deleted. This may cause duplicate issues to be created for this email. Subject <subject>

   Since the were no errors it shouldn't print this to the log.

2. Downloading attachment fails, typically it happens with some mail servers and with very large attachments, the attachment is only partially downloaded it will still be attached to jira issue.
   The issue should be commented on to indicate that attachment processing failed and no partial attachment is added to the issue.
3. Forward email option should be respected when attachment failure occurs