Add cinder_cross_az_attach option

fixes bug 1128546

This patch adds the cinder_cross_az_attach option to toggle
whether volume attachments are allowed between zones, which was
added in Grizzly.

Given the current state of cinder and availability zone documentation
this patch might be a little worthless. However, at least it will
allow understanding of the default behaviour.

Fix minor typo and spelling error.

Change-Id: Idff7a59a726d70e229fcb18d98deb5b38ce649fc
Merge "Add cinder_cross_az_attach option"