Move code that calls out to os-brick for connectors,
encryptors, etc., into volume_utils.
This leaves cinder/utils.py more general-purpose
cinder-wide code, which reduces unnecessary binding
between things like "cinder-manage db" and calls
that load much more of cinder's code (and external
libraries like os-brick).
This also means that some drivers only need to
import volume_utils and not cinder.utils.
Partial-Bug: #1912278
Change-Id: Ib2e2960ca354a47d303e0633c7d84e6da4b55b82
e7b4670516