qemuMigrationDstPrepareStorage: Use 'switch' statement to include all storage types

qemuMigrationDstPrepareStorage: Use 'switch' statement to include all storage types

Decrease the likelyhood that addition of a new storage type will be
forgotten.

This patch also unifies the type check to consult the 'actual' type of
the storage in both cases as the NVMe check looked for the XML declared
type while virStorageSourceIsLocalStorage() looks for the
actual/translated type.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>