Adjust setting of go-build version.
Adjust setting of go-build version.

For ppc64le builds set the default GO_BUILD_VER to "latest".
Allow GO_BUILD_VER to be override by the make caller's environment.

Signed-off-by: David Wilder <c99dc2f4f8d2e2b13883c936de59f520004971aa@us.ibm.com>

projectcalico/k8s-policy,projectcalico/k8s-policy