swim: follow-ups for SWIM anti-entropy

* fix some obvious errors in swim test utils;

* fix a bug with NULL URI garbage on recfg;

* fix typos in a comment and in a log message in swim.c;

* do not start any timers in swim_cfg. Indeed, round timer should
  start only when at least one new member is added except self,
  and it is already done in swim_new_member;

* log not only round begin, but each round step - it helps in
  debug, but does not affect production anyway because the logs
  are verbose;

* in SWIM's event loop log new watch value instead of the old
  one - turned out, that new is more useful for debug;

* log 'process <name> component' inside swim_process_<name>()
  functions. It is needed for failure detection, where a log of
  kind 'process failure detection' says nothing - much better to
  say 'process ping from', or 'process ack';

* in swim tests instead of swim_cluster_wait_...(max_steps) use
  swim_cluster_wait_...(timeout). Step count restriction appeared
  to be useful for anti-entropy being equal to number of round
  steps, but it is not so once failure detection appears. Replies
  for failure detection requests does not depend on SWIM
  heartbeat and affect step count in a not trivial way - it makes
  test writing, debugging and supporting much harder.

Follow-up for 03b9a6e9