Python: skip root on venv detection

Virtual environments on the root level are uncommon and can cause issues
on some linux distros.

Fixes: QTCREATORBUG-27976
Change-Id: I266f1b321c1c2d2b4b416acf3f34ce8c1d686219
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/python/pythonsettings.cpp

@@ -930,7 +930,7 @@ QList<Interpreter> PythonSettings::detectPythonVenvs(const FilePath &path)
                     dir.cdUp();
                 }
             }
-        } while (dir.cdUp());
+        } while (dir.cdUp() && !(dir.isRoot() && Utils::HostOsInfo::isAnyUnixHost()));
     }
     return result;
 }