Update to use go modules (#671)

This includes updates to CI config, vendor files, etc.
I've hard-coded the k8s depedency at 1.13.4 to keep it inline with what
we currently have and to make sure a another run of `go mod tidy`
doesn't accidentally update it to an unexpected version.

Thanks to hectorj2f for carrying this along.

go.mod

@@ -0,0 +1,65 @@
+module github.com/virtual-kubelet/virtual-kubelet
+
+go 1.12
+
+require (
+	contrib.go.opencensus.io/exporter/ocagent v0.4.12
+	github.com/davecgh/go-spew v1.1.1
+	github.com/docker/spdystream v0.0.0-20170912183627-bc6354cbbc29 // indirect
+	github.com/elazarl/goproxy v0.0.0-20190421051319-9d40249d3c2f // indirect
+	github.com/elazarl/goproxy/ext v0.0.0-20190421051319-9d40249d3c2f // indirect
+	github.com/evanphx/json-patch v4.1.0+incompatible // indirect
+	github.com/gogo/protobuf v1.2.1 // indirect
+	github.com/golang/groupcache v0.0.0-20181024230925-c65c006176ff // indirect
+	github.com/google/btree v1.0.0 // indirect
+	github.com/google/go-cmp v0.2.0
+	github.com/google/gofuzz v1.0.0 // indirect
+	github.com/googleapis/gnostic v0.1.0 // indirect
+	github.com/gorilla/mux v1.6.2
+	github.com/gregjones/httpcache v0.0.0-20180305231024-9cad4c3443a7 // indirect
+	github.com/hashicorp/golang-lru v0.5.1 // indirect
+	github.com/imdario/mergo v0.3.4 // indirect
+	github.com/inconshreveable/mousetrap v1.0.0 // indirect
+	github.com/json-iterator/go v1.1.6 // indirect
+	github.com/konsorten/go-windows-terminal-sequences v1.0.2 // indirect
+	github.com/mitchellh/go-homedir v1.1.0
+	github.com/modern-go/reflect2 v1.0.1 // indirect
+	github.com/onsi/ginkgo v1.8.0 // indirect
+	github.com/onsi/gomega v1.5.0 // indirect
+	github.com/peterbourgon/diskv v2.0.1+incompatible // indirect
+	github.com/pkg/errors v0.8.1
+	github.com/sirupsen/logrus v1.4.1
+	github.com/spf13/cobra v0.0.2
+	github.com/spf13/pflag v1.0.3
+	github.com/stretchr/testify v1.3.0 // indirect
+	go.opencensus.io v0.20.2
+	golang.org/x/crypto v0.0.0-20190325154230-a5d413f7728c // indirect
+	golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3 // indirect
+	golang.org/x/oauth2 v0.0.0-20190402181905-9f3314589c9a // indirect
+	golang.org/x/sys v0.0.0-20190403152447-81d4e9dc473e // indirect
+	golang.org/x/text v0.3.1-0.20181227161524-e6919f6577db // indirect
+	golang.org/x/time v0.0.0-20190308202827-9d24e82272b4 // indirect
+	google.golang.org/api v0.3.2 // indirect
+	google.golang.org/genproto v0.0.0-20190404172233-64821d5d2107 // indirect
+	google.golang.org/grpc v1.20.0 // indirect
+	gopkg.in/inf.v0 v0.9.1 // indirect
+	gopkg.in/yaml.v2 v2.2.2 // indirect
+	gotest.tools v0.0.0-20181223230014-1083505acf35
+	k8s.io/api v0.0.0-20181213150558-05914d821849
+	k8s.io/apimachinery v0.0.0-20181127025237-2b1284ed4c93
+	k8s.io/apiserver v0.0.0-20181213151703-3ccfe8365421 // indirect
+	k8s.io/client-go v0.0.0-20181213151034-8d9ed539ba31
+	k8s.io/klog v0.1.0
+	k8s.io/kube-openapi v0.0.0-20190510232812-a01b7d5d6c22 // indirect
+	k8s.io/kubernetes v1.13.4
+	k8s.io/utils v0.0.0-20180801164400-045dc31ee5c4 // indirect
+	sigs.k8s.io/yaml v1.1.0 // indirect
+)
+
+replace k8s.io/client-go => k8s.io/client-go v0.0.0-20190228174230-b40b2a5939e4
+
+replace k8s.io/api => k8s.io/api v0.0.0-20190222213804-5cb15d344471
+
+replace k8s.io/apimachinery => k8s.io/apimachinery v0.0.0-20190221213512-86fb29eff628
+
+replace k8s.io/kubernetes => k8s.io/kubernetes v1.13.4