Interface for Format functions

[guilhem]

Currently, Interface only support "mount" functions:

mount-utils/mount.go

Line 39 in d561b6c

type Interface interface {

To simply CSI test and mocking
Can we create a new Interface for all "Format" functions?
like:

mount-utils/mount.go

Line 189 in d561b6c

func (mounter *SafeFormatAndMount) FormatAndMount(source string, target string, fstype string, options []string) error {