Pybob sets /lib as library prefix in env.sh, even on 64bit only systems

[d3rhans]

Pybob sets the library path on Linux systems to .../lib/..., hardcoded in environment.py, line 32. If packages are installed on a 64bit only system, they will reside in .../lib64/... as determined by cmake. This leads to a non-working env.sh file after the bolero installation, see rock-learning/bolero#111

I assume the correct way to do this, is to query the DESTDIR system configuration variable of distutils. I'll test this on different systems (Fedora and Ubuntu) and provide a pull request.

Workaround: Till this is fixed, manually change the path in env.sh to the correct installation directory.