Manila retry function does not accept random periods

[Alyson]

The current manila.utils.retry() function always uses fixed numbers to define the time to wait before performing the next attempts. This behavior can make the retries of multiple requisitions coincide many times and cause concurrency errors repeatedly.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/219851

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/219851
Committed: https://git.openstack.org/cgit/openstack/manila/commit/?id=8dc3863e102828ce8bf3111d24ad74acd2dfd405
Submitter: Jenkins
Branch: master

commit 8dc3863e102828ce8bf3111d24ad74acd2dfd405
Author: Alyson Rosa <email address hidden>
Date: Wed Sep 2 13:28:30 2015 -0300

    Adds retry function to HNAS driver

    Multiple requests sent to HNAS can cause concurrency problems
    and that ends up with 'SSC failed connection' errors. This
    patch adds a retry decorator to _execute in HDS HNAS Manila
    driver to fix this problem.

    The current retry functionality in Manila always uses fixed
    numbers to define the time to wait before performing the next
    attempts. This behavior can make the retries of multiple
    requests to collide in each attempt as they will wait the
    same amount of time and try to use the same resource together
    again. So additionally, this patch changes the behavior of
    manila.utils.retry() to receive a parameter that allows the
    function to implement randomly generated wait intervals.

    Change-Id: Ib862f62517fcc8816781204b902119e9b20121e0
    Closes-bug: 1491550