``Backend._ensure_backend_available`` converts the URL object to string

[Rodolfo Alonso]

In [1], ``Backend._ensure_backend_available`` is converting a ``url.URL`` to string to then parse it again to obtain a ``url.URL`` object again.

* Before SQLAlchemy 2.0, the ``URL.__str__`` method was calling "render_as_string" method with "hide_password=False".
* In SQLAlchemy 2.0 [3], the `URL.__str__`` doesn't exist and `URL.__repr__`` is called instead. However, in this case the password is hidden. That means the new URL object created has the string "***" as password instead of the original string.

This issue has been detected in the Neutron experimental CI, in the "neutron-functional-with-sqlalchemy-master" job [4].

[1]https://github.com/openstack/oslo.db/blob/94d6e24ca19b0116eed00d5ccdb8a538918c6dcf/oslo_db/sqlalchemy/provision.py#L262
[2]https://github.com/sqlalchemy/sqlalchemy/blob/cdad8ab375ab5d04c52f7be7ce1c85f588d8355e/lib/sqlalchemy/engine/url.py#L559
[3]https://github.com/sqlalchemy/sqlalchemy/blob/c7ce7ff0225fe0ddaf63f0706429b885410de365/lib/sqlalchemy/engine/url.py#L610
[4]https://fa67ce491574b958f29b-7b9374470c0105283123d1c69dc66ebe.ssl.cf2.rackcdn.com/878526/1/experimental/neutron-functional-with-sqlalchemy-master/cc86a0a/testr_results.html

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/oslo.db/+/878642

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/oslo.db/+/878642
Committed: https://opendev.org/openstack/oslo.db/commit/da4f13e7345653eba8aab5b8aceeaeff7367989e
Submitter: "Zuul (22348)"
Branch: master

commit da4f13e7345653eba8aab5b8aceeaeff7367989e
Author: Rodolfo Alonso Hernandez <email address hidden>
Date: Mon Mar 27 15:12:06 2023 +0200

    Do not convert to string ``url.URL`` objects

    The SQLAlchemy method ``url.make_url`` accepts strings and ``url.URL``
    object types. By default, oslo.db was converting any object to string
    before calling ``url.make_url``, that parses this string. Since
    SQLAlchemy 2.0, the ``url.URL.__str__`` method is removed and the
    ``url.URL.__repr__`` method returns a string with the password hidden.

    The new utility method checks what type of object is passed and only
    if the object is not a string nor a ``url.URL`` object, is converted
    to a string.

    Closes-Bug: #2012928
    Change-Id: I84f13f378f83e2a55078370ae2b4787f00982c23

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/oslo.db 13.0.0 release.