[glusterfs] Disable CGO to build static binary
[glusterfs] Disable CGO to build static binary

`glusterfs-simple-provisioner` binary was dynamically linked
unless disable CGO_ENABLED flag. So that container image doesn't
work because alpine image doesn't contain dependent libraries.

This patch disable CGO_ENABLED flag to build container image
correctly.

humblec/external-storage,childsb/external-storage,humblec/external-storage,humblec/external-storage,kubernetes-incubator/external-storage,kubernetes-incubator/external-storage,kubernetes-incubator/external-storage,childsb/external-storage,childsb/external-storage