mgr/volumes: use `volume_exception_to_retval` as a decorator

mgr/volumes: use `volume_exception_to_retval` as a decorator

When used as a decorator, it saves one indented try-catch block inside the decorated method.
This can be applied to most of the methods in the file, subject to a separate refactoring commit

Signed-off-by: Leonid Usov <leonid.usov@ibm.com>
(cherry picked from commit 78afc6136118e14e2cf6a5651bfe11777c9881a4)