Support Go modules

This is mostly just adding `go.mod` and `go.sum`.  But the generate
scripts don't entirely work well with modules:

 - `rm -rf $TEMPDIR` won't work, because `${GOPATH}/pkg/mod`
   directories are chmod o-w (this can be worked around by calling
   chmod).

 - The various `go` commands put other packages in 'go.mod', which we
   don't want.

Instead of trying to adjust all of the scripts, just set
GO111MODULE=off in the Makefile when calling them.

Makefile

@@ -13,23 +13,23 @@ test-examples:
 
 .PHONY: generate
 generate: _output/kubernetes _output/bin/protoc _output/bin/gomvpkg _output/bin/protoc-gen-gofast _output/src/github.com/golang/protobuf
-	./scripts/generate.sh
-	go run scripts/register.go
+	GO111MODULE=off ./scripts/generate.sh
+	GO111MODULE=off go run scripts/register.go
 	cp scripts/json.go.partial apis/meta/v1/json.go
 
 .PHONY: verify-generate
 verify-generate: generate
 	./scripts/git-diff.sh
 
 _output/bin/protoc-gen-gofast:
-	./scripts/go-install.sh \
+	GO111MODULE=off ./scripts/go-install.sh \
 		https://github.com/gogo/protobuf \
 		github.com/gogo/protobuf \
 		github.com/gogo/protobuf/protoc-gen-gofast \
 		tags/v0.5
 
 _output/bin/gomvpkg:
-	./scripts/go-install.sh \
+	GO111MODULE=off ./scripts/go-install.sh \
 		https://github.com/golang/tools \
 		golang.org/x/tools \
 		golang.org/x/tools/cmd/gomvpkg \

go.mod

@@ -0,0 +1,7 @@
+module github.com/ericchiang/k8s
+
+require (
+	github.com/golang/protobuf v1.2.0
+	golang.org/x/net v0.0.0-20190125091013-d26f9f9a57f3
+	golang.org/x/text v0.3.0 // indirect
+)

go.sum

@@ -0,0 +1,6 @@
+github.com/golang/protobuf v1.2.0 h1:P3YflyNX/ehuJFLhxviNdFxQPkGK5cDcApsge1SqnvM=
+github.com/golang/protobuf v1.2.0/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
+golang.org/x/net v0.0.0-20190125091013-d26f9f9a57f3 h1:ulvT7fqt0yHWzpJwI57MezWnYDVpCAYBVuYst/L+fAY=
+golang.org/x/net v0.0.0-20190125091013-d26f9f9a57f3/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
+golang.org/x/text v0.3.0 h1:g61tztE5qeGQ89tm6NTjjM9VPIm088od1l6aSorWRWg=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=