Use clibmseed to parse INFO responses in MiniSEED

Previously, INFO responses were "parsed" like this:

```python
lenmsr = len(slpacket.msrecord)
data = slpacket.msrecord[64:lenmsr]
```

I.e. the MiniSEED headers were just assumed to be 8 bytes. This causes problems with e.g. IRIS Ringserver, (which only uses 7 bytes), effectively cutting off the first 8 charaters of the response.

This pull request fixes that by parsing the MiniSEED packet using `clibmseed`. I also added a test case including two actual packets sent by GEOFON and IRIS SeedLink servers.