CINDER_SECURE_DELETE previously iniset volume_clear to none as a
side effect, however secure_delete is not documented in cinder.
Now using CINDER_VOLUME_CLEAR outright. CINDER_SECURE_DELETE is
supported but now deprecated.
Change-Id: Ic8694cf16654c23b27d23853a9f06ddf1050fa93
Closes-Bug: #1450159