Fix cinder concurrency issues on rtstool

Fix cinder concurrency issues on rtstool

Since there's no synchronized access to configfs in rtslib it can happen
that rtstool or rtslib access an element that no longer exists because
it has been removed just in the middle of a loop by another Cinder
request.

This results in quite a different number of exceptions:
- .dump()
- KeyError
- IOError
- RTSLibError on storage_object

This patch synchronizes access to all rtstool calls that access or
modify configfs using utils.synchronized decorator.

Change-Id: I341a10da54ab01be68a0cae843f35e5c841c6d81
Closes-Bug: #1460692