Change lock reason -> info

This makes it more apparent that the information passed in isn't
required nor will it conform to any standard. There may be call sites
that can't provide good contextual info, and we don't want to count on
that value.

state/state.go

@@ -42,7 +42,9 @@ type StatePersister interface {
 }
 
 // Locker is implemented to lock state during command execution.
+// The optional info parameter can be recorded with the lock, but the
+// implementation should not depend in its value.
 type Locker interface {
-	Lock(reason string) error
+	Lock(info string) error
 	Unlock() error
 }