Quote usernames in the sshd_log if necessary

If the incoming username contains a space it would throw off any
program reading the log file.  Instead quote the value so that a
parser could detect the quoted entry and recover.

Change-Id: If74e8c1f6820df9ba9369b039e6285fefff62549
Signed-off-by: Shawn O. Pearce <sop@google.com>

gerrit-sshd/src/main/java/com/google/gerrit/sshd/SshLog.java

@@ -308,7 +308,12 @@ class SshLog implements LifecycleListener {
       Object val = event.getMDC(key);
       buf.append(' ');
       if (val != null) {
-        buf.append(val);
+        String s = val.toString();
+        if (0 <= s.indexOf(' ')) {
+          buf.append(QuotedString.BOURNE.quote(s));
+        } else {
+          buf.append(val);
+        }
       } else {
         buf.append('-');
       }