havana: nova/xen Enable live block migration when using iSCSI volumes

[Tom Fifield]

https://review.openstack.org/25419 adds extra support for xen in nova

    Enable live block migration when using iSCSI volumes

    Fix for bug 1160323.

    DocImpact
    Depends on a version of XAPI supporting relax-xsm-sr-check.
    Currently no release versions support this, so the change at
    https://github.com/xen-org/xen-api/pull/1116 would need to be applied
    to the source to enable this. XenServer 6.2 is expected to
    support this mode, and possibly some future hotfixes for XenServer 6.1.

    It also depends on a configuration change which must be documented and added to devstack:
    * Set "relax-xsm-sr-check = true" in /etc/xapi.conf

    This commit makes the following changes:
    * Attach the SR on the destination host prior to migrate
    * Returns the SR-ref from the pre_migrate call (API change)
    * Populates the XS VDI map with the sr-ref on the destination host
    * Removes the connection to the SR from the source host post-migrate
    * Added plugin to determine if iSCSI block migration is enabled

[Tom Fifield (fifieldt)]

This patch is blocked by the need to completely redocument xen.

[Lana (loquacity)]

Closing as out of date. If someone wants to work on this, please create a new bug.