Log Message:
Update ipaddr-py to version 2.1.5. Major changes:

2.1.5
* containment test should always return false on mixed-type tests.

2.1.4
* fix for  issue66 , more invalid IPv6 addresses will be rejected

2.1.3
* fix for  issue61 , incorrect network containment (thanks bw.default)

2.1.2
* Happy Memorial day.
* arithmetic for v4 and v6 address objects and ints ( issue 57 ).
* fix address_exclude issue where excluding an address from itself
  puked.
* make sure addresses and networks don't compare.
* doc-string fixes ( issue60 )
* and masked() method to BaseNet to return a network object with
  the host bits masked out ( issue58 )
* fix v6 subnet representation (email to ipaddr-py-dev)