Remove workaround for bug #1219530

Bug #1219530 has been fixed before Havana. We can remove this workaround.

Closes-Bug: #1307472
Change-Id: Ib0b1abf7d11627045be922f79aff6b80448ccbf4
Validate CIDR given as ip-prefix in security-group-rule-create

There was no validation for the provided ip prefix. This just adds
a simple parse using netaddr and explodes with appropriate message.
Also makes sure ip prefix _is_ cidr (192.168.1.1-->192.168.1.1/32).

Validation occurs at the attribute level (API model) as well as at
the db level, where the ethertype is validated against the ip_prefix
address type.

Unit test cases added - bad prefix, unmasked prefix and incorrect
ethertype. Also adds attribute test cases for the added
convert_ip_prefix_to_cidr method

Change-Id: I71fb8c887963a122a5bd8cfdda800026c1cd3954
Closes-Bug: 1255338
Merge "Remove workaround for bug #1219530"
Merge "Validate CIDR given as ip-prefix in security-group-rule-create"