fix live migration in progress hard code

[lvmxh]

now in code the migration in progress is hard-code.
such as:
           filter(~models.Migration.status.in_(['accepted', 'confirmed',
                                                 'reverted', 'error',
                                                 'failed'])).\

There maybe many place need this list.

They should share.

After we fixed the depended on bus: https://bugs.launchpad.net/nova/+bug/1549558

we can easy to clean up the migration in progress hard-code.

[lvmxh (shaohef)]

This is also error prone.

Many place have the same hard-code.

It is easy to missing some , when we need to change every "in progress" list.

[Sean Dague (sdague)]

This is really a duplicate of the other issue you filed. Please just work off the one bug.