migration: Create load_setup()/cleanup() methods

We need to do things at load time and at cleanup time.

Signed-off-by: Juan Quintela <quintela@redhat.com>

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Move the printing of the error message so we can print the device
giving the error.
Add call to postcopy stuff
Message-Id: <20170628095228.4661-4-quintela@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>