ssh: more details on failure

In case we fail without output from the ssh command, we should at least
add the exit code or any other failure reason to the error message, and
log it and the cmdline used to the node daemon log.

Reviewed-by: imsnah

lib/ssh.py

@@ -219,6 +219,9 @@ class SshRunner:
       output = retval.output
       if output:
         msg += ": %s" % output
+      else:
+        msg += ": %s (no output)" % retval.fail_reason
+      logging.error("Command %s failed: %s" % (retval.cmd, msg))
       return False, msg
 
     remotehostname = retval.stdout.strip()