Jenkinsfile: set DOCKER_BUILDKIT globally
Jenkinsfile: set DOCKER_BUILDKIT globally

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

estesp/docker,jameszhan/docker,yosifkit/docker,nalind/docker,moul/docker,thaJeztah/docker,jameszhan/docker,jimjag/docker,Ramzec/docker,mahak/docker,bearstech/moby,ibuildthecloud/docker,jvanz/docker,pradipd/moby,konstruktoid/docker-1,kojiromike/docker,moby/moby,kolyshkin/moby,mahak/docker,konstruktoid/docker-upstream,yosifkit/docker,jthelin/docker,cpuguy83/docker,bearstech/moby,cpuguy83/docker,jimjag/docker,trebonian/docker,thaJeztah/docker,kolyshkin/moby,yosifkit/docker,moby/moby,dims/docker,Mokolea/docker,mahak/docker,gnailuy/docker,AkihiroSuda/docker,justincormack/docker,Ramzec/docker,bearstech/moby,djs55/docker,ibuildthecloud/docker,yongtang/docker,jimjag/docker,docker/docker,konstruktoid/docker-upstream,Mokolea/docker,nawawi/docker,SvenDowideit/docker,dims/docker,trebonian/docker,nalind/docker,djs55/docker,trebonian/docker,tmp6154/docker,tmp6154/docker,kojiromike/docker,jameszhan/docker,konstruktoid/docker-1,konstruktoid/docker-1,nawawi/docker,flavio/docker,justincormack/docker,pradipd/moby,paralin/docker,paralin/docker,cpuguy83/docker,ibuildthecloud/docker,pradipd/moby,moby/moby,kojiromike/docker,paralin/docker,moby/moby,dims/docker,nalind/docker,djs55/docker,nawawi/docker,cpuguy83/docker,Ramzec/docker,estesp/docker,yongtang/docker,yongtang/docker,moul/docker,moul/docker,flavio/docker,thaJeztah/docker,jvanz/docker,Mokolea/docker,jvanz/docker,nawawi/docker,flavio/docker,tmp6154/docker,vdemeester/docker,nalind/docker,vdemeester/docker,AkihiroSuda/docker,AkihiroSuda/docker,vdemeester/docker,ibuildthecloud/docker,konstruktoid/docker-upstream,docker/docker,jthelin/docker,docker/docker,thaJeztah/docker,paralin/docker,flavio/docker,trebonian/docker,gnailuy/docker,jimjag/docker,justincormack/docker,konstruktoid/docker-upstream,bearstech/moby,ibuildthecloud/docker,gnailuy/docker,Ramzec/docker,AkihiroSuda/docker,SvenDowideit/docker,mahak/docker,kolyshkin/moby,moul/docker,estesp/docker,yosifkit/docker,SvenDowideit/docker,gnailuy/docker,Mokolea/docker