Use a different sys path for import completions and import type inference

Fix tests of the #1451 pull request

test/completion/on_import.py

@@ -20,8 +20,12 @@ def builtin_test():
 #? ['sqlite3']
 import sqlite3
 
-#? ['classes']
+# classes is a local module that has an __init__.py and can therefore not be
+# found. test can be found.
+#? []
 import classes
+#? ['test']
+import test
 
 #? ['timedelta']
 from datetime import timedel

test/test_inference/test_imports.py

@@ -115,6 +115,8 @@ def test_find_module_not_package_zipped(Script, inference_state, environment):
 def test_import_not_in_sys_path(Script):
     """
     non-direct imports (not in sys.path)
+
+    This is in the end just a fallback.
     """
     a = Script(path='module.py', line=5).goto_definitions()
     assert a[0].name == 'int'