Sentinel: always redirect on master->slave transition.

Sentinel redirected to the master if the instance changed runid or it
was the first time we got INFO, and a role change was detected from
master to slave.

While this is a good idea in case of slave->master, since otherwise we
could detect a failover without good reasons just after a reboot with a
slave with a wrong configuration, in the case of master->slave
transition is much better to always perform the redirection for the
following reasons:

1) A Sentinel may go down for some time. When it is back online there is
no other way to understand there was a failover.
2) Pointing clients to a slave seems to be always the wrong thing to do.
3) There is no good rationale about handling things differently once an
instance is rebooted (runid change) in that case.

src/sentinel.c

@@ -1452,19 +1452,15 @@ void sentinelRefreshInstanceInfo(sentinelRedisInstance *ri, const char *info) {
     if (sentinel.tilt) return;
 
     /* Act if a master turned into a slave. */
-    if ((ri->flags & SRI_MASTER) && role == SRI_SLAVE) {
-        if ((first_runid || runid_changed) && ri->slave_master_host) {
-            /* If it is the first time we receive INFO from it, but it's
-             * a slave while it was configured as a master, we want to monitor
-             * its master instead. */
-            sentinelEvent(REDIS_WARNING,"+redirect-to-master",ri,
-                "%s %s %d %s %d",
-                ri->name, ri->addr->ip, ri->addr->port,
-                ri->slave_master_host, ri->slave_master_port);
-            sentinelResetMasterAndChangeAddress(ri,ri->slave_master_host,
-                                                   ri->slave_master_port);
-            return;
-        }
+    if ((ri->flags & SRI_MASTER) && role == SRI_SLAVE && ri->slave_master_host)
+    {
+        sentinelEvent(REDIS_WARNING,"+redirect-to-master",ri,
+            "%s %s %d %s %d",
+            ri->name, ri->addr->ip, ri->addr->port,
+            ri->slave_master_host, ri->slave_master_port);
+        sentinelResetMasterAndChangeAddress(ri,ri->slave_master_host,
+                                               ri->slave_master_port);
+        return;
     }
 
     /* Act if a slave turned into a master. */