fix broken cluster/sentinel tests by recent commit (#7752)
fix broken cluster/sentinel tests by recent commit (#7752)

2b998de46 added a file for stderr to keep valgrind log but i forgot to
add a similar thing when valgrind isn't being used.
the result is that `glob */err.txt` fails.
ofirluzon/redis,ofirluzon/redis,neomantra/redis,neomantra/redis,yossigo/redis,yossigo/redis,neomantra/redis,soloestoy/redis,soloestoy/redis,yossigo/redis,antirez/redis,ofirluzon/redis,oranagra/redis,neomantra/redis,ctripcorp/redis,PKRoma/redis,ctripcorp/redis,PKRoma/redis,PKRoma/redis,charsyam/redis,ctripcorp/redis,charsyam/redis,yossigo/redis,oranagra/redis,ofirluzon/redis,charsyam/redis,oranagra/redis,PKRoma/redis,charsyam/redis,oranagra/redis,neomantra/redis,PKRoma/redis,soloestoy/redis,antirez/redis,ctripcorp/redis,soloestoy/redis,yossigo/redis,antirez/redis,ofirluzon/redis,oranagra/redis,charsyam/redis,antirez/redis,soloestoy/redis