Revert "Made provider optional in create-service-auth-token command"

This reverts commit 83d6867a9fbd6df39388759d733d1215205666cc.

Conflicts:
	src/cf/api/service_auth_tokens.go
	src/cf/api/service_auth_tokens_test.go
	src/cf/app/app.go
	src/cf/commands/service/create_service_auth_token.go