Fix walkthrough scenario

[mszostok]

Description

Changes proposed in this pull request:

Fix minor bugs in the walkthrough scenario by:

• fixing resources path declarations in kustomization.yaml file (regex in file names is not supported, see: Entry resources from kustomization.yaml supports only relative and absolute paths kubernetes-sigs/kustomize#254)
  previous error:

kustomize build config/default | kubectl apply -f -
Error: loadResMapFromBasesAndResources: rawResources failed to read Resources: Load from path ../rbac/*.yaml failed: open /Users/i331808/workspace/go/src/github.com/jpeeler/podpreset-crd/config/rbac/*.yaml: no such file or directory

• fixing missing dependencies in vendor
  previous error:

make docker-build-webhook

CGO_ENABLED=0 GOOS=linux go build -o ./webhook/webhook ./webhook/
webhook/main.go:31:2: cannot find package "github.com/mattbaird/jsonpatch" in any of:
	/Users/i331808/workspace/go/src/github.com/jpeeler/podpreset-crd/vendor/github.com/mattbaird/jsonpatch (vendor tree)
	/usr/local/Cellar/go/1.10.2/libexec/src/github.com/mattbaird/jsonpatch (from $GOROOT)
	/Users/i331808/workspace/go/src/github.com/mattbaird/jsonpatch (from $GOPATH)
make: *** [docker-build-webhook] Error 1

• fixing sed command to works also on OS X system
  previous error:

updating kustomize image patch file for manager resource
sed -i 's@image: .*@image: '"docker.io/service-catalog/podpreset-controller:latest"'@' ./config/default/manager_image_patch.yaml
sed: 1: "./config/default/manage ...": invalid command code .
make: *** [docker-build] Error 1

[jpeeler]

Thanks for the contribution and validating the implementation in this repo!