an enum with value 0 should be interpreted as False

for example: bool(Enum(off=0, on=1)('off')) is False

Change-Id: Ieb200b4ecf0eed50b657ecc00f73a69810ad828f
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/28586
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

test/test_lib_enum.py

@@ -77,3 +77,9 @@ def test_Enum():
     assert e3.c >= e2.a
     assert e3.b <= e2.b
     assert Enum({'self': 0, 'other': 1})('self') == 0
+
+
+def test_Enum_bool():
+    e = Enum('OffOn', off=0, on=1)
+    assert bool(e(0)) is False
+    assert bool(e(1)) is True