fix(helm): fix tests if tmp directory is on another block device
fix(helm): fix tests if tmp directory is on another block device

Two non-exported helper functions were added to the repo index test
file. They first try to link the file, since this is optimal. If the
link fails a copy occurs.

Fixes #1472

technosophos/deployment-manager,eicnix/helm,adamreese/deployment-manager,technosophos/k8s-helm,michelleN/deployment-manager,adamreese/deployment-manager,qwangrepos/helm,jascott1/helm,kdada/helm,qwangrepos/helm,sushilkm/helm,bradj/helm,rbwsam/helm,appscode/helm,technosophos/deployment-manager,adamreese/deployment-manager,flynnduism/helm,technosophos/deployment-manager,sushilkm/helm,eicnix/helm,technosophos/k8s-helm,fibonacci1729/helm,fibonacci1729/helm,adamreese/helm,SlickNik/helm,michelleN/deployment-manager,technosophos/deployment-manager,bacongobbler/helm,flynnduism/helm,iamzhout/helm,rbwsam/helm,yan234280533/helm,helm/helm,helm/helm,adamreese/helm,adamreese/deployment-manager,FengyunPan/helm,bacongobbler/helm,iamzhout/helm,kdada/helm,thomastaylor312/helm,jascott1/helm,michelleN/deployment-manager,thomastaylor312/helm,michelleN/deployment-manager,yan234280533/helm,adamreese/deployment-manager,appscode/helm,SlickNik/helm,bradj/helm,FengyunPan/helm,technosophos/deployment-manager