Restore osapi_volume_workers config option

osapi_volume_worker was introduced when enabling multi-process API
support for Cinder. However, this config option was accidentally
dropped in commit 464277220ddb800ac69562649fde62e5ca9358c4
(https://review.openstack.org/#/c/67657/20/cinder/service.py).
As a result, the value in cinder.conf wouldn't be honored.  This
change restore this config option.

Closes-bug: #1335295

Change-Id: Ib2d8532d3e6d0f48da0bc4dd6f6e64bfff8973ea
Slow down Storwize driver initialization

Storwize has the limitation that can not burst more than
3 new ssh connection within 1 second.So slow down storwize
driver initialization.

Closes-Bug: #1335722
Change-Id: Id442cd6421ef23b953a3cb45a5f6dd6969064a6e
sync periodic_task fix from incubator

Set the value of time the periodic task was last run to a multiple of
the spacing value rather than the actual last time run. This ensures
tasks runs regularly but avoids synchronizing that interval with other
nodes.

This patch also removes the coalescing of tasks which are _nearby_ (0.2
seconds away).

Changes:

periodic_task
-------------
4dbd3aa Make periodic tasks run on regular spacing interval
21249f1 Fix parenthesis typo misunderstanding in periodic_task

Change-Id: I6c06ae73b18d4425a987a215a050bc70335e490e
Merge "sync periodic_task fix from incubator"
Merge "Restore osapi_volume_workers config option"