Fix volume options

Fix volume options

Change I358c414adb49bba9349f30a1190c2f8b90f13d14 had a few issues. Of
note, packer variables can only be strings, even if they get
interpolated to booleans where needed.

Additionally the volume format can only be specified if
use_block_storage is true and we default to false. This means that if
volume storage is being set then the volume format must be set and it
needs to be set to raw!

Finally, the windows builder did not contain all the extra variables
being defined.

Change-Id: Icb2de795f0ba185a2d758123ec5dd705c86d8980
Signed-off-by: Andrew Grimberg <agrimberg@linuxfoundation.org>