Migration_status being used to hold target info

[Kendall Nelson]

There are several places where migration_status is being used to store info about the migration, i.e. target: + vol_id. migration_status should only be holding string statuses: migrating, error, success, completing, none, etc.

Examples:

 https://github.com/openstack/cinder/blob/e62cb5eac5ee8074235a855b0ccafa1134eecc19/cinder/volume/manager.py#L1619

https://github.com/openstack/cinder/blob/master/cinder/volume/drivers/solidfire.py#L1273-L1275

https://github.com/openstack/cinder/blob/72611dc2137548666f95c9649eb3575e0273821f/cinder/tests/unit/volume/drivers/nec/test_volume.py#L934

This doesn't cause issues at the moment, but it needs to be fixed before the migration_status field can be made into an ovo enum. There are a few drivers that depend on this logic and so they will also need to be updated.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/511737

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/511737
Committed: https://git.openstack.org/cgit/openstack/cinder/commit/?id=a638f483fb41df4f4acc0b0f42d289ba711333e5
Submitter: Zuul
Branch: master

commit a638f483fb41df4f4acc0b0f42d289ba711333e5
Author: Shunei Shiono <email address hidden>
Date: Fri Oct 13 16:02:26 2017 +0900

    NEC driver: Never use target info in migration_status

    NEC driver uses target info in migration_status at volume creation.
    The target info will be deleted from migration_status in future
    cinder version. This patch change the driver not to use target info
    in migration_status.

    Change-Id: I04b188d1300979b3b4b070781c6c2105f638b649
    Partial-Bug: #1706729