Log stack trace if CachingKeyPairProvider hits unexpected exception

Log the stack trace in order to help understanding the bug 563380

Bug: 563380
Change-Id: If993a63ccec5042b10e1d5e945b18f4b5f06d8ff
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.ssh.apache/src/org/eclipse/jgit/internal/transport/sshd/CachingKeyPairProvider.java

@@ -170,7 +170,7 @@ public class CachingKeyPairProvider extends FileKeyPairProvider
 				} catch (CancellationException cancelled) {
 					throw cancelled;
 				} catch (Exception other) {
-					log.warn(other.toString());
+					log.warn(other.getMessage(), other);
 				}
 			}
 			return nextItem != null;