[Integrated] RFR: Use a different (empty) thread prefix for failed automerge PRs

[Robin Westberg]

Changeset: c2bf15e6
Author:    Robin Westberg <rwestberg at openjdk.org>
Date:      2020-03-26 09:34:26 +0000
URL:       https://git.openjdk.java.net/skara/commit/c2bf15e6

Use a different (empty) thread prefix for failed automerge PRs

Reviewed-by: ehelin

! bots/merge/src/main/java/org/openjdk/skara/bots/merge/MergeBot.java
! bots/merge/src/test/java/org/openjdk/skara/bots/merge/MergeBotTests.java
! bots/mlbridge/src/main/java/org/openjdk/skara/bots/mlbridge/ArchiveItem.java
! bots/mlbridge/src/main/java/org/openjdk/skara/bots/mlbridge/ReviewArchive.java
! bots/mlbridge/src/test/java/org/openjdk/skara/bots/mlbridge/MailingListBridgeBotTests.java