Use proper log warning instead of printing to System.err when fetcher.properties is not found

Description

The AbstractFeedFetcher will print the warning directly to System.err. It should
use a proper log instead (especially since the absence of fetcher.properties
does not prevent the feature to work)

Environment

None

Status

Assignee

ROME Jira Lead

Reporter

deleted_user

Labels

None

Participants

None

Affects versions

current

Priority

Major