Jenkinsfile: Z/Power: use buildx
Jenkinsfile: Z/Power: use buildx

Z and Power does not currently work with buildkit so use buildx instead.

Signed-off-by: Brian Goff <dc73d0991b982a8303e713ef531a313af77e242a@gmail.com>

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