rados: add a function for use as a finalizer for any opStep

This utility function avoids having to have a custom finalizer for every
op step. It calls the free() function to release any allocated C memory
the step may have.

Signed-off-by: John Mulligan <jmulligan@redhat.com>

rados/operation.go

@@ -112,6 +112,12 @@ func (o *operation) update(kind opKind, ret C.int) error {
 	}
 }
 
+func opStepFinalizer(s opStep) {
+	if s != nil {
+		s.free()
+	}
+}
+
 // withoutUpdate can be embedded in a struct to help indicate
 // the type implements the opStep interface but has a no-op
 // update function.