daemon/cluster: add a missing Unlock
daemon/cluster: add a missing Unlock

Signed-off-by: Ziheng Liu <f7f149e5a659fc13c80c604a2bf83d2463599785@gmail.com>

Mokolea/docker,jimjag/docker,trebonian/docker,paralin/docker,dims/docker,jameszhan/docker,moul/docker,thaJeztah/docker,jvanz/docker,moby/moby,cpuguy83/docker,kojiromike/docker,jameszhan/docker,justincormack/docker,mahak/docker,cpuguy83/docker,moul/docker,flavio/docker,jameszhan/docker,jthelin/docker,nalind/docker,thaJeztah/docker,gnailuy/docker,nalind/docker,AkihiroSuda/docker,vdemeester/docker,djs55/docker,trebonian/docker,justincormack/docker,dims/docker,konstruktoid/docker-upstream,Mokolea/docker,docker/docker,cpuguy83/docker,docker/docker,ibuildthecloud/docker,thaJeztah/docker,AkihiroSuda/docker,jvanz/docker,paralin/docker,ibuildthecloud/docker,estesp/docker,Mokolea/docker,estesp/docker,kojiromike/docker,docker/docker,yosifkit/docker,Ramzec/docker,vdemeester/docker,Mokolea/docker,paralin/docker,dims/docker,konstruktoid/docker-upstream,nalind/docker,yosifkit/docker,ibuildthecloud/docker,yosifkit/docker,moul/docker,trebonian/docker,ibuildthecloud/docker,jimjag/docker,moul/docker,Ramzec/docker,flavio/docker,jvanz/docker,cpuguy83/docker,trebonian/docker,mahak/docker,konstruktoid/docker-1,estesp/docker,moby/moby,kojiromike/docker,moby/moby,paralin/docker,flavio/docker,vdemeester/docker,gnailuy/docker,djs55/docker,flavio/docker,mahak/docker,AkihiroSuda/docker,yosifkit/docker,nalind/docker,bearstech/moby,bearstech/moby,mahak/docker,konstruktoid/docker-upstream,konstruktoid/docker-upstream,nawawi/docker,bearstech/moby,AkihiroSuda/docker,Ramzec/docker,nawawi/docker,nawawi/docker,thaJeztah/docker,Ramzec/docker,moby/moby,justincormack/docker,gnailuy/docker,ibuildthecloud/docker,nawawi/docker,konstruktoid/docker-1,bearstech/moby,jimjag/docker,konstruktoid/docker-1,jimjag/docker,djs55/docker,jthelin/docker,gnailuy/docker