* WIP adds network subnetting functions
* adds functions to convert between netmask and masklen
* adds functions to verify netmask and masklen
* adds function to dtermine network and subnet from address / mask pair
* network_common: add a function to get the first 48 bits in a IPv6 address.
ec2_group: only use network bits of a CIDR.
* Add tests for CIDRs with host bits set.
* ec2_group: add warning if CIDR isn't the networking address.
* Fix pep8.
* Improve wording.
* fix import for network utils
* Update tests to use pytest instead of unittest
* add test for to_ipv6_network()
* Fix PEP8
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