recovery: add logging of recovered buckets

This patch introduces logging of buckets' ids which were recovered
during recovery stage of storage.

Part of #212

NO_DOC=bugfix

Author: mrForza

test/storage-luatest/storage_1_1_1_test.lua

@@ -188,6 +188,7 @@ rebalancer_recovery_group.test_no_logs_while_unsuccess_recovery = function(g)
         g.replica_1_a:exec(function() ivshard.storage.recovery_wakeup() end)
         t.assert(g.replica_1_a:grep_log('Finish bucket recovery step, 2 ' ..
                                         'sending buckets are recovered among'))
+        t.assert(g.replica_1_a:grep_log('Recovered buckets: %[1,2%]'))
     end)
     assert_bucket_is_transferred(g.replica_2_a, g.replica_1_a,
                                  hanged_bucket_id_1)

vshard/storage/init.lua

@@ -932,6 +932,7 @@ local function recovery_step_by_type(type)
     local recovered = 0
     local total = 0
     local start_format = 'Starting %s buckets recovery step'
+    local recovered_buckets = {}
     for _, bucket in _bucket.index.status:pairs(type) do
         lfiber.testcancel()
         total = total + 1
@@ -1002,11 +1003,13 @@ local function recovery_step_by_type(type)
                      bucket_id, bucket.status, remote_bucket.status, peer_id)
         end
         is_step_empty = false
+        table.insert(recovered_buckets, bucket_id)
 ::continue::
     end
     if recovered > 0 then
         log.info('Finish bucket recovery step, %d %s buckets are recovered '..
                  'among %d', recovered, type, total)
+        log.info('Recovered buckets: %s', json_encode(recovered_buckets))
     end
     return total, recovered
 end