[Feature Request] Mirror rotation against server failure

[opk12]

Guidelines

• I have searched the issue tracker for open and closed issues that are similar to the feature request I want to file, without success.
• I'm on the latest version.
• I'm not using a test build (alpha/beta/release-candidate).
• This issue contains only one feature request.

Problem Description

The DNS for a mirror is failing, so the metadata download fails.

Proposed Solution

The firewall log shows 25 attempts for the same mirror before the syncing aborts. What about trying a mirror 3 times and then switching to another one?

Alternatives Considered

Mirror rotation was added in 2bc0e29 to address #163 which is focused on doing round-robin to reduce the server load. The focus in this ticket is redundancy for fault tolerance.

Relevant information

Current impl seems to be