s3/client: check for available port before starting minio server

there is chance that the default port of 9000 has been used on the
host running the test, in that case, we should try to use another
available port.

so, in this change, we try ports in the ranges of [9000, 9000+1000),
and use the first one which is not connectable.

Fixes #14985
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>

test/pylib/minio_server.py

@@ -128,11 +128,29 @@ class MinioServer:
         return {'Statement': statement,
                 'Version': '2012-10-17'}
 
+    async def _is_port_available(self, port: int) -> bool:
+        try:
+            _, writer = await asyncio.open_connection('localhost', port)
+            writer.close()
+            await writer.wait_closed()
+            return False
+        except OSError:
+            # likely connection refused
+            return True
+
+    async def _find_available_port(self, min_port: int, max_port: int) -> int:
+        assert min_port < max_port
+        for port in range(min_port, max_port):
+            if await self._is_port_available(port):
+                return port
+        raise RuntimeError(f'failed to find available port in [{min_port}, {max_port})')
+
     async def start(self):
         if self.srv_exe is None:
             self.logger.info("Minio not installed, get it from https://dl.minio.io/server/minio/release/linux-amd64/minio and put into PATH")
             return
 
+        self.port = await self._find_available_port(self.port, self.port + 1000)
         self.address = await self.hosts.lease_host()
         self.log_file = self.log_filename.open("wb")
         os.environ['S3_SERVER_ADDRESS_FOR_TEST'] = f'{self.address}'