Catch exceptions when computing image checksums. Ref https://github.com/GNS3/gns3-server/issues/2228

gns3server/web/web_server.py

@@ -240,9 +240,12 @@ class WebServer:
 
         loop = asyncio.get_event_loop()
         with concurrent.futures.ProcessPoolExecutor(max_workers=1) as pool:
-            log.info("Computing image checksums...")
-            await loop.run_in_executor(pool, list_images, "qemu")
-            log.info("Finished computing image checksums")
+            try:
+                log.info("Computing image checksums...")
+                await loop.run_in_executor(pool, list_images, "qemu")
+                log.info("Finished computing image checksums")
+            except OSError as e:
+                log.warning("Could not compute image checksums: {}".format(e))
 
     async def _on_startup(self, *args):
         """