Move the code that (possibly) generates filename of NVRAM VAR
store into a single function so that it can be re-used later.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NLaszlo Ersek <lersek@redhat.com>
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>