enhance systemtools.py to also support POWER systems

fixes issues reported in https://github.com/hpcugent/easybuild/issues/32 by @chwilk
why is this a list? 
```python
cpu_freq_reg = re.compile(r'^(?:cpu MHz|clock)\s*:\s*(?P<cpu_freq>[0-9.]+)', re.M)
```
is all you need. if you want to add the output on x86 and power, then add a line of such output as a comment