[migration] added delta dirs import step

migration/castor/exporttapepool.sh

@@ -57,6 +57,7 @@ set -e
 tapepool_castor_to_cta.py -t $1 -v $2 -i $3 $4
 
 # execute the EOS metadata import
+eos-import-dirs --delta     # should there be any
 eos-import-files
 
 # terminate the export