Do the following for NSXv locking:
- Drop external=True from get_lock() calls: this is redundant as
locking wrapper appends this anyway.
- Add locking for distributed router module.
- Use edge-id as lock id when locking various edge attributes.
- Drop the use of lock_file_prefix as it is not supported by
distributed locking.
Change-Id: I13115f65a89d5fae507f87f7fb1ac096089e385a
34475f4fc4