mysql-router must support multiple instantiations

[David Ames]

In the case of the Nova Cells nova-cloud-controller must be connected to two or more databases. See the focal enablement PR for nova-cell-controller [0].

This means there must be multiple instantiations of mysql-router on the nova-cloud-controller unit. Currently it does not support this.

TRIAGE:

mysql-router
* Working directory /var/lib/mysql/mysqlrouter needs to be instance specific
* Systemd file needs to be instance specific
* 1 + n versions will need to listen on a separate port

interface-mysql-shared and client charms
* Currently there is no concept of port number, 3306 is assumed

mysql-innodb-cluster
* All mysql-router instances on the same IP should get the same mysqlrouter user and password to avoid allowed unit collisions

[0] https://review.opendev.org/#/c/718484/11

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/725410

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/725411

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/725410
Committed: https://git.openstack.org/cgit/openstack/charm-interface-mysql-shared/commit/?id=c31027400aea53bc2900b6694a458370b8f3f86c
Submitter: Zuul
Branch: master

commit c31027400aea53bc2900b6694a458370b8f3f86c
Author: David Ames <email address hidden>
Date: Mon May 4 14:51:43 2020 -0700

    Specify the port for Shared DB connections

    Prior to this change there was no way to specify a port for mysql
    connections. Add this to the Shared DB connection information.

    Change-Id: Iafcc106fca44479e89b4b66a0a3988ffeee01f04
    Closes-Bug: #1876188

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/725411
Committed: https://git.openstack.org/cgit/openstack/charm-mysql-router/commit/?id=403216591530f6330aa75c583e988471dac1948a
Submitter: Zuul
Branch: master

commit 403216591530f6330aa75c583e988471dac1948a
Author: David Ames <email address hidden>
Date: Mon May 4 14:39:20 2020 -0700

    Allow for multiple instantiations of mysql-router

    Before this change it was not possible to run more than one
    instantiation of mysql-router on a single unit. The Nova cells
    deployments require nova-cloud-controller to be connected to two
    different databases, therefore, requiring two instantiations of
    mysql-router.

    This change includes all the necessary steps to run multiple
    instantiations of mysql-router on a single unit.

    Review and merge charm-helpers PR:
    https://github.com/juju/charm-helpers/pull/469

    Closes-Bug: #1876188
    Depends-On: Iafcc106fca44479e89b4b66a0a3988ffeee01f04
    Change-Id: I76d1bfdccf9a551188c9f86c06ee0a22c07d47cf