Designate charm does not support quota management

[Tytus Kurek]

At the moment designate charm does not support quota management feature.

Ideally, quotas should be set through the admin API. The reasoning is as follows:
* v1 API is deprecated
* quota extension is not supported in v2 API in Mitaka
* admin API was designed exactly for this purpose - admin operations and analytics

Thus, I would like to propose to enable the admin API and quota extension for the admin API. However, as the admin API will remain in an "experimental" state forever (it will never become stable), I would suggest to enable it through configurable charm option.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/552477

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/552477
Committed: https://git.openstack.org/cgit/openstack/charm-designate/commit/?id=41a34e63f6c8879d40f17abfd9cff90549ac8adf
Submitter: Zuul
Branch: master

commit 41a34e63f6c8879d40f17abfd9cff90549ac8adf
Author: Tytus Kurek <email address hidden>
Date: Fri May 11 10:40:25 2018 +0200

    Add option to enable admin API and quotas

    This patchset adds an option which can be used to enable an
    experimental admin API for Designate and quota extension for it.

    Change-Id: I3c1da2a53e52a50b19a569d16e995d5e20ed3f4d
    Closes-Bug: 1755451