qns: enable multiconnect test and explicitly create the log directory
qns: enable multiconnect test and explicitly create the log directory

- Add "multiconnect" target to test case
- Fix file not found error of transfer tests

Error message:
```
./run_endpoint.sh: line 58: /logs/log.txt: No such file or directory
```
cloudflare/quiche,cloudflare/quiche,cloudflare/quiche