xds/kokoro: install go 1.17, and retry go build (#5015)

test/kokoro/xds.sh

@@ -13,7 +13,13 @@ shopt -s extglob
 branch="${branch//[[:space:]]}"
 branch="${branch##remotes/origin/}"
 shopt -u extglob
-go build
+# Install a version of Go supported by gRPC for the new features, e.g.
+# errors.Is()
+curl --retry 3 -O -L https://go.dev/dl/go1.17.3.linux-amd64.tar.gz
+sudo tar -C /usr/local -xf go1.17.3.linux-amd64.tar.gz
+sudo ln -s /usr/local/go/bin/go /usr/bin/go
+# Retry go build on errors (e.g. go get connection errors), for at most 3 times
+for i in 1 2 3; do go build && break || sleep 5; done
 popd
 
 git clone -b "${branch}" --single-branch --depth=1 https://github.com/grpc/grpc.git