Default crush map should use straw2

[Sandor Zeestraten]

The default crush algorithm used by the charms is `straw`, while `straw2` was the new default in the Hammer release (http://docs.ceph.com/docs/mimic/rados/operations/crush-map/#hammer-crush-v4).

Deployments with `straw` will need to migrate to `straw2` in order to utilise newer features in Luminous such as the mgr balance plugin (https://ceph-users.ceph.narkive.com/fFMZOiMg/error-creating-compat-weight-set-with-mgr-balancer-plugin).

Migration impact:
Changing a bucket type from straw to straw2 will result in a reasonably small amount of data movement, depending on how much the bucket item weights vary from each other. When the weights are all the same no data will move, and when item weights vary significantly there will be more movement.

Offending line: https://github.com/openstack/charm-ceph-mon/blob/master/lib/ceph/crush_utils.py#L27

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/670232
Committed: https://git.openstack.org/cgit/openstack/charms.ceph/commit/?id=5f095b59cd078a76aeeca22cb5a7b34f9fae9e67
Submitter: Zuul
Branch: master

commit 5f095b59cd078a76aeeca22cb5a7b34f9fae9e67
Author: Chris MacNaughton <email address hidden>
Date: Thu Jul 11 08:00:06 2019 +0200

    Update default CRUSH algorithm to straw2

    straw2 has been the default CRUSH algorithm since hammer
    and Ubuntu Xenial ships with Jewel, meaning that straw2
    is the default in all current LTS releases.

    Change-Id: I6fa4072eb33d763aca5721ee9fdd30b60d468a44
    Closes-Bug: #1836092

[Alex Kavanagh (ajkavanagh)]

This charms.ceph code has been merged into ceph-mon and released as part of the 19.10 release.

[OpenStack Infra (hudson-openstack)]

Change abandoned by "Chris MacNaughton <email address hidden>" on branch: master
Review: https://review.opendev.org/c/openstack/charm-ceph-mon/+/670233
Reason: This fix merged in via another sync