make pg upgrade more safe

entrypoint.postgres.sh.tmpl

@@ -1,5 +1,7 @@
 #!/bin/bash
 
+set -e
+
 MIGRATION_MARKER=$PGDATA/migration_in_progress
 OLDDATA=$PGDATA/old_data
 NEWDATA=$PGDATA/new_data
@@ -21,7 +23,7 @@ if [ -n "$DATA_VERSION" -a "$PG_MAJOR" != "$DATA_VERSION" ]; then
   echo "shuffling around"
   gosu postgres mkdir $OLDDATA $NEWDATA
   chmod 700 $OLDDATA $NEWDATA
-  mv $PGDATA/* $OLDDATA/
+  mv $PGDATA/* $OLDDATA/ || true
   touch $MIGRATION_MARKER
   echo "running initdb"
   # abuse entrypoint script for initdb by making server error out