add missing yamls in controllers/nginx

[harryge00]

examples/ingress.yaml and examples/default/rc-default.yaml are missing. And I did not find the latter...

Add default-backend.yaml because it is used.

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[k8s-reviewable]

This change is 

[coveralls]

Coverage remained the same at 43.613% when pulling 4e1ae0efb7bae2d20b1cfca20d518697fb486419 on harryge00:add-yaml-to-nginx-controller into 2d6f811 on kubernetes:master.

[coveralls]

Coverage remained the same at 43.613% when pulling 4e1ae0efb7bae2d20b1cfca20d518697fb486419 on harryge00:add-yaml-to-nginx-controller into 2d6f811 on kubernetes:master.

[coveralls]

Coverage decreased (-0.02%) to 43.588% when pulling 6dd1b0b on harryge00:add-yaml-to-nginx-controller into 2d6f811 on kubernetes:master.

[aledbf]

@harryge00 thanks!