--provider global flag for kompose

Now a user can select a provider using global flag
--provider=openshift to select openshift provider
or --provider-kubernetes to select kubernetes provider
if nothing is provided kubernetes is the default provider.

Fixes #179

pkg/kobject/kobject.go

@@ -125,6 +125,7 @@ type ConvertOptions struct {
 	Replicas               int
 	InputFile              string
 	OutFile                string
+	Provider               string
 }
 
 // ServiceConfig holds the basic struct of a container