Hardcode part_power for swift ring builder

[OpenStack Infra]

https://review.openstack.org/239412
commit 22e51270d56a650fdb3b76549e07cf93be31bb4b
Author: Matthew Mosesohn <email address hidden>
Date: Mon Oct 26 14:52:47 2015 +0300

    Hardcode part_power for swift ring builder

    The default part_power for 3 controllers should
    be 10. Previous deployments calculated the part_power
    of 3 controllers to 10, so this should be preserved
    for future deployments.

    For custom deployments which require a different part_power,
    it should be set in swift_hash in the key 'ring_part_power'.

    Removed calc_ring_part_power provider because it will no
    longer be used.

    DocImpact: Should advise users before upgrading from a
    prior release about swift ring part_power.
    Change-Id: Ic7f8f6824712cc2bb5b530fe1300c9a3ac4ce302
    Closes-Bug: #1498368