The new configuration storwize_preferred_host_site was introduced in
volume type for hyperswap feature on Queens release. Actually, the
host_site is related to host rather than volume.
This patch removes the parameter storwzie_preferred_host_site from
volume type configuration and updates it from StrOpt to DictOpt in cinder
back-end configuration.
Closes-Bug: 1742866
Change-Id: Ie1df4cc45c2d1f72f33beea7ddc5bb3797a34728