gql-cli add signal handlers to catch ctrl-c and close cleanly (#276)

Now the gql-cli script works on Python 3.6 too

Author: leszekhanusz

scripts/gql-cli

@@ -1,6 +1,7 @@
 #!/usr/bin/env python3
 import asyncio
 import sys
+from signal import SIGINT, SIGTERM
 
 from gql.cli import get_parser, main
 
@@ -9,8 +10,23 @@ parser = get_parser(with_examples=True)
 args = parser.parse_args()
 
 try:
-    # Execute the script
-    exit_code = asyncio.run(main(args))
+    # Create a new asyncio event loop
+    loop = asyncio.new_event_loop()
+    asyncio.set_event_loop(loop)
+
+    # Create a gql-cli task with the supplied arguments
+    main_task = asyncio.ensure_future(main(args), loop=loop)
+
+    # Add signal handlers to close gql-cli cleanly on Control-C
+    for signal in [SIGINT, SIGTERM]:
+        loop.add_signal_handler(signal, main_task.cancel)
+
+    # Run the asyncio loop to execute the task
+    exit_code = 0
+    try:
+        exit_code = loop.run_until_complete(main_task)
+    finally:
+        loop.close()
 
     # Return with the correct exit code
     sys.exit(exit_code)