test: fix flaky bucket_ref test

One of the cases didn't expect that the rebalancer would move the
bucket right from under the test's nose. The patch pauses the
rebalancer for the time of this case execution.

NO_DOC=test

test/rebalancer/bucket_ref.result

@@ -35,13 +35,19 @@ util.push_rs_filters(test_run)
 _ = test_run:switch('box_1_a')
 ---
 ...
+vshard.storage.rebalancer_disable()
+---
+...
 vshard.storage.bucket_force_create(1, 100)
 ---
 - true
 ...
 _ = test_run:switch('box_2_a')
 ---
 ...
+vshard.storage.rebalancer_disable()
+---
+...
 vshard.storage.bucket_force_create(101, 100)
 ---
 - true
@@ -290,6 +296,18 @@ vshard.storage.buckets_info(1)
 -- function taking the lock is bucket_send, so to test that a
 -- manual bucket_send is called before rebalancer.
 --
+vshard.storage.rebalancer_enable()
+---
+...
+_ = test_run:switch('box_2_a')
+---
+...
+vshard.storage.rebalancer_enable()
+---
+...
+_ = test_run:switch('box_1_a')
+---
+...
 keep_lock = true
 ---
 ...

test/rebalancer/bucket_ref.test.lua

@@ -15,8 +15,10 @@ util.push_rs_filters(test_run)
 -- allow bucket transfer or GC during a request execution.
 --
 _ = test_run:switch('box_1_a')
+vshard.storage.rebalancer_disable()
 vshard.storage.bucket_force_create(1, 100)
 _ = test_run:switch('box_2_a')
+vshard.storage.rebalancer_disable()
 vshard.storage.bucket_force_create(101, 100)
 _ = test_run:switch('box_1_a')
 
@@ -95,6 +97,10 @@ vshard.storage.buckets_info(1)
 -- function taking the lock is bucket_send, so to test that a
 -- manual bucket_send is called before rebalancer.
 --
+vshard.storage.rebalancer_enable()
+_ = test_run:switch('box_2_a')
+vshard.storage.rebalancer_enable()
+_ = test_run:switch('box_1_a')
 keep_lock = true
 send_result = nil
 -- To make first bucket_send keeping rw_lock it is necessary to