Redis test fails on unstable: Expected condition '[s -1 sync_partial_ok] > 0' to be true

Hello @antirez !

With current head of unstable branch, make test fails on integration/replication-psync.

I have gcc version 6.2.0 20160901 (Debian 6.2.0-3) on Linux debian 4.7.0-1-amd64 #1 SMP Debian 4.7.2-1 (2016-08-28) x86_64 GNU/Linux

                  The End

Execution time of different units:
  0 seconds - unit/printver
  0 seconds - unit/type/incr
  0 seconds - unit/scan
  0 seconds - unit/auth
  1 seconds - unit/quit
  1 seconds - unit/protocol
  1 seconds - unit/keyspace
  2 seconds - unit/multi
  6 seconds - unit/type/hash
  6 seconds - unit/type/set
  8 seconds - unit/type/zset
  8 seconds - unit/sort
  9 seconds - unit/other
  1 seconds - integration/rdb
  9 seconds - unit/type/string
  1 seconds - integration/convert-zipmap-hash-on-load
  1 seconds - unit/pubsub
  1 seconds - integration/logging
  1 seconds - unit/slowlog
  0 seconds - unit/introspection
  4 seconds - integration/aof
  10 seconds - unit/expire
  1 seconds - unit/limits
  1 seconds - unit/bitfield
  13 seconds - unit/type/list
  3 seconds - unit/bitops
  5 seconds - unit/maxmemory
  6 seconds - unit/scripting
  15 seconds - unit/type/list-2
  1 seconds - unit/lazyfree
  6 seconds - unit/introspection-2
  4 seconds - unit/memefficiency
  17 seconds - integration/replication-2
  12 seconds - unit/geo
  15 seconds - unit/hyperloglog
  28 seconds - unit/dump
  27 seconds - integration/replication-3
  35 seconds - integration/replication-4
  53 seconds - unit/obuf-limits
  73 seconds - unit/aofrw
  90 seconds - integration/replication
  95 seconds - unit/type/list-3
  107 seconds - integration/replication-psync

!!! WARNING The following tests failed:

*** [err]: Test replication partial resync: ok psync (diskless: yes, reconnect: 1) in tests/integration/replication-psync.tcl
Expected condition '[s -1 sync_partial_ok] > 0' to be true ([s -1 sync_partial_ok] > 0)
Cleanup: may take some time... OK
Makefile:227: recipe for target 'test' failed
make[1]: *** [test] Error 1
make[1]: Leaving directory '/home/cengiz/Code/c/redis/src'
Makefile:6: recipe for target 'test' failed
make: *** [test] Error 2

If you don't mind, I'd like to work on this.

I'd like to improve my knowledge about redis internals and contribute at the same time

:beers: