Remove python-netaddr requirement

Remove python-netaddr as a DevStack (stack.sh) requirement,
this does not change any individual project requirements.

Specifically it replaces address_in_net() and adds cidr2netmask()
and maskip() functions.

Change-Id: Ic604437fde2e057faced40a310ab282f3eb27726
Merge branch 'screen-stop' into dt-test
Merge branch 'doc-shocco-cleanup' into dt-test
Merge branch 'update-usb-tools' into dt-test