bump go to 1.16, other misc fixes

- add selinux relabling to release.sh
- use same go version in root

Signed-off-by: Casey Callendrello <cdc@redhat.com>

scripts/release.sh

@@ -16,7 +16,7 @@ rm -Rf ${SRC_DIR}/${RELEASE_DIR}
 mkdir -p ${SRC_DIR}/${RELEASE_DIR}
 mkdir -p ${OUTPUT_DIR}
 
-$DOCKER run -ti -v ${SRC_DIR}:/go/src/github.com/containernetworking/plugins --rm golang:1.15-alpine \
+$DOCKER run -ti -v ${SRC_DIR}:/go/src/github.com/containernetworking/plugins:z --rm golang:1.16-alpine \
 /bin/sh -xe -c "\
     apk --no-cache add bash tar;
     cd /go/src/github.com/containernetworking/plugins; umask 0022;