pkg/generator: only generate deepcopy

[fanminshi]

change the auto-gen script to only generate the deepcopy files for a operator project.

[fanminshi]

Manual Test:

$ operator-sdk generate k8s
Generating deepcopy funcs

$ tree pkg/
pkg/
├── apis
│   └── cache
│       └── v1alpha1
│           ├── doc.go
│           ├── register.go
│           ├── types.go
│           └── zz_generated.deepcopy.go
└── stub
    └── handler.go

[fanminshi]

cc/ @hasbro17

[hasbro17]

LGTM