Defrag: fix test false positive.
Defrag: fix test false positive.

Apparently 1.4 is too low compared to what you get in certain setups
(including mine). I raised it to 1.55 that hopefully is still enough to
test that the fragmentation went down from 1.7 but without incurring in
issues, however the test setup may be still fragile so certain times this
may lead to false positives again, it's hard to test for these things
in a determinsitic way.

Related to #3786.

charsyam/redis,nnog/redis,antirez/redis,PKRoma/redis,PKRoma/redis,rogerchina/redis,PKRoma/redis,spinlock/redis,nnog/redis,soloestoy/redis,rogerchina/redis,charsyam/redis,ctripcorp/redis,antirez/redis,yossigo/redis,soloestoy/redis,ofirluzon/redis,antirez/redis,neomantra/redis,oranagra/redis,GitHubMota/redis,GitHubMota/redis,rogerchina/redis,Sciumo/redis,soloestoy/redis,Sciumo/redis,yossigo/redis,Sciumo/redis,pmem/redis,ctripcorp/redis,hgl888/redis,neomantra/redis,neomantra/redis,PKRoma/redis,yossigo/redis,ctripcorp/redis,ofirluzon/redis,ctripcorp/redis,oranagra/redis,kensou97/redis,GitHubMota/redis,antirez/redis,yossigo/redis,charsyam/redis,charsyam/redis,hgl888/redis,spinlock/redis,ofirluzon/redis,Sciumo/redis,ofirluzon/redis,GitHubMota/redis,ofirluzon/redis,PKRoma/redis,pmem/redis,spinlock/redis,soveran/redis,spinlock/redis,yossigo/redis,oranagra/redis,oranagra/redis,kensou97/redis,nnog/redis,rogerchina/redis,kensou97/redis,soloestoy/redis,kensou97/redis,soveran/redis,neomantra/redis,soloestoy/redis,soveran/redis,hgl888/redis,pmem/redis,charsyam/redis,soveran/redis,oranagra/redis,nnog/redis,neomantra/redis,hgl888/redis,pmem/redis