Port floating_ip_dns extention to v2.1

This patch ports floating_ip_dns extention from v2 to v2.1,
and have v2 unit test cases shared between v2.1 and v2.
Partially implements blueprint v2-on-v3-api

Change-Id: Ia1316697c141fde2b431ba79aebae5986687a4fa
Remove `domain` from floating-ip-dns-create-or-update-req body

`domain` is passed in the url req id, so it is unuseful in the
request body, remove it and v3 api-samples.

Change-Id: If8bdfb7fc928daaf01c9612c97c6b391d3139505
typo in the policy.json "rule_admin_api"

policy.json has "rule_admin_api" string instead of
the "rule:admin_api" which causes ValueError.

The typo recently introduced by
 4bb34182fe28c89686c8a23ddcfc8e9128d289b5.

Change-Id: I232adfca033e9365927cf2abd62d391337fae429
Closes-Bug: #1385225
Merge "typo in the policy.json "rule_admin_api""
Merge "Port floating_ip_dns extention to v2.1"
Merge "Remove `domain` from floating-ip-dns-create-or-update-req body"