script: trim RTT log data on dictionary parser

The fact that log data captured with RTT has a header, like the
following, impedes the parser to parse the data properly

```
Trying ::1...
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
SEGGER J-Link V8.24 - Real time terminal output
SEGGER J-Trace PRO V4.0, SN=XXXX
Process: JLinkExe
```

Signed-off-by: Leonardo Bispo <l.bispo@live.com>