Special case UnknownHostKey during replication

Signed-off-by: Shawn O. Pearce <sop@google.com>
diff --git a/src/main/java/com/google/gerrit/git/PushQueue.java b/src/main/java/com/google/gerrit/git/PushQueue.java
index af94cfd..7c6c035 100644
--- a/src/main/java/com/google/gerrit/git/PushQueue.java
+++ b/src/main/java/com/google/gerrit/git/PushQueue.java
@@ -19,6 +19,7 @@
 import com.google.gwtjsonrpc.server.XsrfException;
 import com.google.gwtorm.client.OrmException;
 
+import com.jcraft.jsch.JSchException;
 import com.jcraft.jsch.Session;
 
 import org.slf4j.Logger;
@@ -176,6 +177,12 @@
       log.error("Cannot replicate to " + op.uri, e);
       return;
     } catch (TransportException e) {
+      final Throwable cause = e.getCause();
+      if (cause instanceof JSchException
+          && cause.getMessage().startsWith("UnknownHostKey:")) {
+        log.error("Cannot replicate to " + op.uri + ": " + cause.getMessage());
+        return;
+      }
       log.error("Cannot replicate to " + op.uri, e);
       return;
     } finally {