[GPartition] Rename the input argument for dispatch (#931)

*Issue #, if available:*

*Description of changes:*

We now reverse the meaning of the original ``--do-dispatch`` input
argument.

Successfully test with 
```
python3 -m graphstorm.gpartition.dist_partition_graph \
    --input-path ./test-gsprocessing/ \
    --metadata-filename updated_row_counts_metadata.json \
    --output-path ./gspartition-example/ \
    --num-parts 1 \
    --dgl-tool-path ./dgl/tools \
    --partition-algorithm random \
    --ip-config ip_list.txt \
    --ssh-port 2222 \
    --partition-assignment-only
```

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copy, and redistribute this contribution, under the terms of your
choice.

---------

Co-authored-by: xiang song(charlie.song) <[email protected]>

python/graphstorm/gpartition/dist_partition_graph.py

@@ -142,7 +142,7 @@ def main():
                  part_end - part_start,
     )
 
-    if args.do_dispatch:
+    if not args.partition_assignment_only:
         run_build_dglgraph(
             args.input_path,
             part_assignment_dir,
@@ -165,9 +165,11 @@ def main():
             dirs_exist_ok=True,
         )
 
-
-    logging.info('Partition assignment and DGL graph creation took %f seconds',
+    if not args.partition_assignment_only:
+        logging.info('Partition assignment and DGL graph creation took %f seconds',
                  time.time() - start)
+    else:
+        logging.info('Partition assignment took %f seconds', time.time() - start)
 
 def parse_args() -> argparse.Namespace:
     """Parses arguments for the script"""
@@ -189,7 +191,9 @@ def parse_args() -> argparse.Namespace:
     argparser.add_argument("--ip-config", type=str,
                            help=("A file storing a list of IPs, one line for "
                                 "each instance of the partition cluster."))
-    argparser.add_argument("--do-dispatch", action='store_true')
+    argparser.add_argument("--partition-assignment-only", action='store_true',
+                           help="Only generate partition assignments for nodes, \
+                                 the process will not build the partitioned DGL graph")
     argparser.add_argument("--logging-level", type=str, default="info",
                            help="The logging level. The possible values: debug, info, warning, \
                                    error. The default value is info.")