make the S2E paths for WPG, mirror_data  relative

in S2E environment the script runs in modules/prop directory and we can use instead 

```
if isS2E:
    sys.path.insert(0,'/data/S2E/packages/WPG/')
    mirror_data_dir = '/data/S2E/modules/prop/data_common'
else:
```

the following relative paths:

```
if isS2E:
    sys.path.insert(0,'../../packages/WPG/')
    mirror_data_dir = 'data_common'
else:
```
