tests(lxd): avoid failure on multiple calls to --show-log

Cope with repeated calls to lxc console --show-log which exits 1
with the error "no such file or directory" when the log entries
have already been processed and no new log entries exist.

Preserve lxc_log on the client instance and return former log content
on lxd platforms when "no such file or directory" runtime errors are
raised

tests/integration_tests/util.py

@@ -538,10 +538,20 @@ def get_console_log(client: "IntegrationInstance"):
         console_log = client.instance.console_log()
     except NotImplementedError:
         pytest.skip("NotImplementedError when requesting console log")
+    except RuntimeError as e:
+        if "open : no such file or directory" in str(e):
+            if hasattr(client, "lxc_log"):
+                return client.lxc_log
+        raise e
     if console_log is None:
         pytest.skip("Console log has not been setup")
     if console_log.lower().startswith("no console output"):
         pytest.fail("no console output")
+    if PLATFORM in ("lxd_vm", "lxd_container"):
+        # Preserve non empty console log on lxc platforms because
+        # lxc console --show-log can only be called once and the log is flushed
+        # Mulitple calls to --show-log error on "no such file or directory"
+        client.lxc_log = console_log  # type: ignore[attr-defined]
     return console_log