Attach secondary disk for migration

Signed-off-by: Stev Witzel <switzel@pivotal.io>
Migrate disk on update

Signed-off-by: Stev Witzel <switzel@pivotal.io>
DiskPool.Size -> DiskPool.DiskSize

Signed-off-by: Stev Witzel <switzel@pivotal.io>
Detach primary disk after migration

Signed-off-by: Stev Witzel <switzel@pivotal.io>
Update current disk after migration

Signed-off-by: Stev Witzel <switzel@pivotal.io>
Update warden manifest

to reflect recent changes in warden cpi release

Signed-off-by: Stev Witzel <switzel@pivotal.io>