add zip_safe flag to setup, to silence multitude of warnings

without the `zip_safe` flag set to `False`, a whole bunch of warnings are spit out when installing easybuild-framework

```
zip_safe flag not set; analyzing archive contents...
easybuild.__init__: module references __path__
easybuild.test.modules: module references __file__
easybuild.test.options: module references __file__
easybuild.toolchains.__init__: module references __path__
easybuild.toolchains.compiler.__init__: module references __path__
easybuild.toolchains.fft.__init__: module references __path__
easybuild.toolchains.linalg.__init__: module references __path__
easybuild.toolchains.mpi.__init__: module references __path__
easybuild.tools.config: module references __file__
easybuild.tools.options: module references __path__
easybuild.tools.version: module references __file__
easybuild.tools.toolchain.utilities: module references __file__
vsc.utils.fancylogger: module MAY be using inspect.stack
vsc.utils.generaloption: module MAY be using inspect.stack
```

see also http://stackoverflow.com/questions/8362510/getting-rid-of-the-easy-install-message-module-references-file