solve race in expiration test (#10192)
solve race in expiration test (#10192)

Failed on a non-valgrind run. on this line:
```
assert_equal 0 [$slave exists k]
```
the condition in `keyIsExpired` is `now > when`.
so if the test is really fast, maybe it can get to EXISTS exactly 1000 milliseconds after the
expiration was set, and the key isn't yet gone)
charsyam/redis,charsyam/redis,antirez/redis,neomantra/redis,PKRoma/redis,soloestoy/redis,neomantra/redis,yossigo/redis,PKRoma/redis,oranagra/redis,yossigo/redis,soloestoy/redis,oranagra/redis,yossigo/redis,neomantra/redis,PKRoma/redis,ofirluzon/redis,oranagra/redis,PKRoma/redis,charsyam/redis,neomantra/redis,soloestoy/redis,ofirluzon/redis,ofirluzon/redis,neomantra/redis,charsyam/redis,charsyam/redis,oranagra/redis,antirez/redis,ofirluzon/redis,oranagra/redis,antirez/redis,antirez/redis,yossigo/redis,soloestoy/redis,ofirluzon/redis,yossigo/redis,soloestoy/redis,PKRoma/redis