storage: introduce on_master_enable service

Before this patch the `rebalancer` and `recovery` service could start
just right after master switch (by `auto` master detection or manual
reconfiguration) before the master had time to sync its vclock with
other replicas in replicaset. It could lead to doubled buckets according
to "Doubled buckets RFC".

To fix it we introduce a new storage service - `on_master_enable`
service. If master is changed in replicaset, this service is triggered
and waits until newly elected master syncs its vclock with other
replicas. Other storage services - `rebalancer` and `recovery` can't
start until `on_master_enable` set `M.buckets_are_in_sync`.

Also we change `storage/storage.test`, `storage/recovery.test`,
`storage-luatest/log_verbosity_2_2_test` and `router/router.test` so
that they wouldn't failed. Now `rebalancer` and `recovery` services
don't start immediately after master switch and it can shake some tests.

Part of #214

NO_TEST=bugfix
NO_DOC=bugfix

Author: mrForza

test/router/router.result

@@ -435,9 +435,25 @@ vshard.router.buckets_info(0, 3)
 _ = test_run:cmd('start server storage_2_a')
 ---
 ...
+_ = test_run:switch('storage_2_a')
+---
+...
+test_run:wait_log('storage_2_a', 'New master has synchronized with other replicas')
+---
+- New master has synchronized with other replicas
+...
+vshard.storage.rebalancer_wakeup()
+---
+...
+vshard.storage.recovery_wakeup()
+---
+...
 --
 -- gh-26: API to get netbox by bucket identifier.
 --
+_ = test_run:switch('router_1')
+---
+...
 vshard.router.route(vshard.consts.DEFAULT_BUCKET_COUNT + 100)
 ---
 - null

test/router/router.test.lua

@@ -162,10 +162,14 @@ end)
 util.check_error(vshard.router.call, 1, 'read', 'echo', {123})
 vshard.router.buckets_info(0, 3)
 _ = test_run:cmd('start server storage_2_a')
-
+_ = test_run:switch('storage_2_a')
+test_run:wait_log('storage_2_a', 'New master has synchronized with other replicas')
+vshard.storage.rebalancer_wakeup()
+vshard.storage.recovery_wakeup()
 --
 -- gh-26: API to get netbox by bucket identifier.
 --
+_ = test_run:switch('router_1')
 vshard.router.route(vshard.consts.DEFAULT_BUCKET_COUNT + 100)
 util.check_error(vshard.router.route, 'asdfg')
 util.check_error(vshard.router.route)

test/storage-luatest/log_verbosity_2_2_test.lua

@@ -119,7 +119,7 @@ test_group.test_rebalancer_do_not_spam_same_errors = function(g)
         end
     end)
     local msg = "Error during downloading rebalancer states"
-    g.replica_1_a:wait_log_exactly_once(msg, {timeout = 0.1,
+    g.replica_1_a:wait_log_exactly_once(msg, {timeout = 1,
         on_yield = function() ivshard.storage.rebalancer_wakeup() end})
     g.replica_2_a:exec(function()
         ivshard.storage.rebalancer_request_state = _G.old_call