xenapi: Always set other_config for VDIs

The existing code only set `other_config` on a VDI when it was created using
`create_vdi`. This patch updates the code so that `other_config` is also set
when a VDI is created from a dom0 plugin or during a migration.

Also included is a one-time script to set the other_config for existing
VDIs that were affected by this bug.

Fixes bug 1162029

Change-Id: I4fa856754487f77ce9c8e39d45eee7ea5187123e
Merge "xenapi: Always set other_config for VDIs"