IDEA-132199 Fix Git get repo for python projects that are also installed in virtualenv

For a python project that is also installed in virutalenv, and has a non-git parent directory, git4idea will try to get the VCS root using a library specific logic, failed to find the correct root, thus failed to find the correct repository.The git branch pop thus failed to pop up when called.

------ Original bug report description ------
Assuming a project structure of following:
workspace
| module_A (library home) 
| module_B (library home)
| module_C
| non_python_module 
Where module A and B are installed on project's virtualenv, module C isn't installed, all four modules are 4 separate git root, and workspace has no vcs root.

Then when module_A  or module_B  is selected, the git branches dialog will not pop out when selecting VCS>Git>Branches... (right click>Git>Repository>Branches... doesn't work either)

The dialog would pop up when module_C  or non_python_module  is selected, and the dialog would still correctly recognise all 4 repositories.

see https://youtrack.jetbrains.com/issue/IDEA-132199