Tests: fix unmonitored servers. (#7756)
Tests: fix unmonitored servers. (#7756)

There is an inherent race condition in port allocation for spawned
servers. If a server fails to start because a port is taken, a new port
is allocated. This fixes a problem where the logs are not truncated and
as a result a large number of unmonitored servers are started.
charsyam/redis,charsyam/redis,PKRoma/redis,ctripcorp/redis,soloestoy/redis,oranagra/redis,antirez/redis,charsyam/redis,PKRoma/redis,yossigo/redis,ctripcorp/redis,PKRoma/redis,neomantra/redis,yossigo/redis,yossigo/redis,antirez/redis,soloestoy/redis,neomantra/redis,PKRoma/redis,ctripcorp/redis,neomantra/redis,oranagra/redis,charsyam/redis,soloestoy/redis,ofirluzon/redis,yossigo/redis,ofirluzon/redis,soloestoy/redis,neomantra/redis,PKRoma/redis,yossigo/redis,ofirluzon/redis,antirez/redis,soloestoy/redis,ofirluzon/redis,ofirluzon/redis,oranagra/redis,oranagra/redis,ctripcorp/redis,neomantra/redis,antirez/redis,charsyam/redis,oranagra/redis