Test the TensorFlow installation location using inspect

[eerwitt]

While testing an installation I executed python -c 'import site; print("\n".join(site.getsitepackages()))' from within a virtualenv environment. This raised the same error mentioned in #392.

According to pypa/virtualenv#355 this is an issue with their custom site implementation and may not be updated soon.

I updated the command in the documentation to output the directory where TensorFlow is installed using inspect.

import os
import inspect
import tensorflow

print(os.path.dirname(inspect.getfile(tensorflow)))

[tensorflow-jenkins]

Can one of the admins verify this patch?

[tensorflow-jenkins]

Can one of the admins verify this patch?

[tensorflow-jenkins]

Can one of the admins verify this patch?

[martinwicke]

Can you squash your commits?