test: flaky box/rtree_rect.test.lua test

[avtikhon]

Tarantool version:
Tarantool 1.10.6-21-gff298cd0d
Target: Darwin-x86_64-RelWithDebInfo
Build options: cmake . -DCMAKE_INSTALL_PREFIX=/usr/local -DENABLE_BACKTRACE=ON
Compiler: /Library/Developer/CommandLineTools/usr/bin/cc /Library/Developer/CommandLineTools/usr/bin/c++
C_FLAGS: -Wno-unknown-pragmas -fexceptions -funwind-tables -fno-omit-frame-pointer -fno-stack-protector -fno-common -msse2 -std=c11 -Wall -Wextra -Wno-strict-aliasing -Wno-char-subscripts -Werror
CXX_FLAGS: -Wno-unknown-pragmas -fexceptions -funwind-tables -fno-omit-frame-pointer -fno-stack-protector -fno-common -msse2 -std=c++11 -Wall -Wextra -Wno-strict-aliasing -Wno-char-subscripts -Werror

OS version:
OSX

Bug description:
https://gitlab.com/tarantool/tarantool/-/jobs/555919569

 [021] --- box/rtree_rect.result	Tue Apr 28 09:12:13 2020
 [021] +++ box/rtree_rect.reject	Sun May 17 11:58:21 2020
 [021] @@ -13,22 +13,22 @@
 [021]  ...
 [021]  s:insert{2,{5,5,10,10}}
 [021]  ---
 [021] -- [2, [5, 5, 10, 10]]
 [021] +- [2]
 [021]  ...
 [021]  s:insert{3,{0,0,5,5}}
 [021]  ---
 [021] -- [3, [0, 0, 5, 5]]
 [021] +- [3]
 [021]  ...
 [021]  -- select all records
 [021]  s.index.spatial:select({}, {iterator = 'ALL'})
 [021]  ---
 [021] -- - [2, [5, 5, 10, 10]]
 [021] -  - [3, [0, 0, 5, 5]]
 [021] +- - [2]
 [021] +  - [3]
 [021]  ...
 [021]  -- select records belonging to rectangle (0,0,5,5)
 [021]  s.index.spatial:select({0,0,5,5}, {iterator = 'LE'})
 [021]  ---
 [021] -- - [3, [0, 0, 5, 5]]
 [021] +- - [3]
 [021]  ...
 [021]  -- select records strict belonging to rectangle (0,0,5,5)
 [021]  s.index.spatial:select({0,0,5,5}, {iterator = 'LT'})

Steps to reproduce:

Optional (but very desirable):

• coredump
• backtrace
• netstat