Adding an ingress tls secret with a non matching certificate and private key break at least the nginx-controller permanently until the offending secret is deleted.
In that case nginx refuses to start/reload with an error like this:
```
Error: exit status 1
2017/06/13 12:16:53 [emerg] 51#51: SSL_CTX_use_PrivateKey_file("/ingress-controller/ssl/monsoon3-tls-baremetal-3-eu-de-1-cloud-sap.pem") failed (SSL: error:0B080074:x509 certificate routines:X509_check_private_key:key values mismatch)
nginx: [emerg] SSL_CTX_use_PrivateKey_file("/ingress-controller/ssl/tls-baremetal-3-example-com.pem") failed (SSL: error:0B080074:x509 certificate routines:X509_check_private_key:key values mismatch)
nginx: configuration file /tmp/nginx-cfg728491545 test failed
```
Generates a Self signed certificate for default vhost if the secret doesn't exists
modified: core/pkg/ingress/controller/backend_ssl.go
modified: core/pkg/ingress/controller/controller.go
modified: core/pkg/net/ssl/ssl.go