TLS configuration helpers applicable to non-API services

[Frode Nordahl]

The TLS configuration helpers are a property of the ``OpenStackCharm`` class which is appropriate and make them available to non-API OpenStack services such as ``ceilometer`` and ``neutron-dynamic-routing`` as well as not strictly speaking OpenStack services such as ``rabbitmq`` and others.

However, they were originally in the ``HAOpenStackCharm`` class and later moved [0], and unfortunately the helpers carried over assumptions about placement of certificate files.

I think the move was appropriate but the helpers could have been adapted to their new home by providing configurability of certificate placement in the ``OpenStackCharm`` helper and then overriding that to the present defaults in the inherited helper in ``HAOpenStackCharm``.

0: https://review.opendev.org/#/c/623295/

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/678598
Committed: https://git.openstack.org/cgit/openstack/charms.openstack/commit/?id=954bbf623d932c7e181b1c4d472f61ca7a4cf643
Submitter: Zuul
Branch: master

commit 954bbf623d932c7e181b1c4d472f61ca7a4cf643
Author: Frode Nordahl <email address hidden>
Date: Mon Aug 26 10:20:45 2019 +0200

    Move TLS related helpers to ``OpenStackCharm`` base class

    TLS configuration is applicable to non-API services too.

    Retains compability with the existing usage pattern by extending
    the helpers with current defaults in the ``HAOpenStackCharm``
    class.

    Deprecates references to the Keystone interface as a source of
    certificate data. This has been removed from the Keystone charm:
    openstack/charm-keystone/commit/17b24e7fde8e4c8c276a4f392cbae0d1d0ed2615

    Reactive handling counterparts:
    Depends-On: I007275c041ca5465664a6b5d441e56c0316c405d
    Depends-On: I12f45236632b608e07fdd35d31b90b84ca92eb1f

    Change-Id: I8a72acd451dd21e1b042b7f71f6d98e164737ac1
    Closes-Bug: #1840899