test.py: manager: add server_get_returncode() method

The method return None if Scylla process is still running or returncode.
If there is no Scylla process launched then raise NoSuchProcess exception.

test/pylib/manager_client.py

@@ -32,6 +32,10 @@ import asyncio
 logger = logging.getLogger(__name__)
 
 
+class NoSuchProcess(Exception):
+    ...
+
+
 class ManagerClient():
     """Helper Manager API client
     Args:
@@ -626,3 +630,12 @@ class ManagerClient():
 
     async def server_get_exe(self, server_id: ServerNum) -> str:
         return await self.client.get_json(f"/cluster/server/{server_id}/exe")
+
+    async def server_get_returncode(self, server_id: ServerNum) -> int | None:
+        match await self.client.get_json(f"/cluster/server/{server_id}/returncode"):
+            case "NO_SUCH_PROCESS":
+                raise NoSuchProcess(f"No process found for {server_id=}")
+            case "RUNNING":
+                return None
+            case returncode:
+                return int(returncode)

test/pylib/scylla_cluster.py

@@ -1482,6 +1482,7 @@ class ScyllaClusterManager:
         add_put('/cluster/server/{server_id}/wipe_sstables', self._cluster_server_wipe_sstables)
         add_get('/cluster/server/{server_id}/sstables_disk_usage', self._server_get_sstables_disk_usage)
         add_get('/cluster/server/{server_id}/process_status', self._server_get_process_status)
+        add_get('/cluster/server/{server_id}/returncode', self._server_get_returncode)
 
     async def _manager_up(self, _request) -> bool:
         return self.is_running
@@ -1821,6 +1822,14 @@ class ScyllaClusterManager:
     async def _server_get_exe(self, request: aiohttp.web.Request) -> str:
         return str(await self._server_get_attribute(request, "exe"))
 
+    async def _server_get_returncode(self, request: aiohttp.web.Request) -> str:
+        if cmd := await self._server_get_attribute(request=request, attribute="cmd"):
+            returncode = cmd.returncode
+            if returncode is None:
+                return "RUNNING"
+            return cmd.returncode
+        return "NO_SUCH_PROCESS"
+
     async def _cluster_server_wipe_sstables(self, request: aiohttp.web.Request):
         data = await request.json()
         server_id = ServerNum(int(request.match_info["server_id"]))