Ignore PortNotFound exceptions on lockless delete

Modifies the delete_ports_by_device_id method to
ignore PortNotFound exceptions because it has no
protection against concurrent operations deleting
the same ports that it's trying to delete.

Closes-Bug: #1293657
Change-Id: Icbcded149364a0e231ae811a440a691518bf20ad
Merge "Ignore PortNotFound exceptions on lockless delete"