Don't analyze call to attributes present in several members of union types

It prevents false positives in checking argument types and argument
lists. We may add multiple analyze call results for this case in the
future.

python/testData/inspections/PyArgumentListInspection/unionTypeAttributeCall.py

@@ -0,0 +1,21 @@
+class C1:
+    def foo(self, x):
+        return self
+
+
+class C2:
+    def foo(self, x, y):
+        return self
+
+
+def f():
+    """
+    :rtype: C1 | C2
+    """
+    pass
+
+
+f().foo()  # XXX: Ignore this false negative as for now
+f().foo(1)
+f().foo(1, 2)
+f().foo(1, 2, 3)  # XXX: Ignore this false negative as well