Rpm version fix - revert using `rpm` for parsing

Reasons: 
- use `grep`/`sed` instead of `rpm`, it prints the version string
for each subpackage
- `rpm` does some dependency evaluation and fails when not runnign in `C` locale:

```
rpm --specfile --qf "%{VERSION}" yast2-storage.spec
chyba: line 122: Illegal char in: Requires:	libstorage-devel = balíček libstorage-devel není nainstalován
chyba: dotaz na spec soubor yast2-storage.spec selhal, nemohu parsovat
```

Although running in `C` locale helps, it seems that `rpm` does too much work and the simple `grep` and `sed` seems to be a better approach...