Falsy values in COMPOSE_CONVERT_WINDOWS_PATHS are properly recognized

Signed-off-by: Joffrey F <joffrey@docker.com>

tests/unit/config/environment_test.py

@@ -0,0 +1,40 @@
+# encoding: utf-8
+from __future__ import absolute_import
+from __future__ import print_function
+from __future__ import unicode_literals
+
+from compose.config.environment import Environment
+from tests import unittest
+
+
+class EnvironmentTest(unittest.TestCase):
+    def test_get_simple(self):
+        env = Environment({
+            'FOO': 'bar',
+            'BAR': '1',
+            'BAZ': ''
+        })
+
+        assert env.get('FOO') == 'bar'
+        assert env.get('BAR') == '1'
+        assert env.get('BAZ') == ''
+
+    def test_get_undefined(self):
+        env = Environment({
+            'FOO': 'bar'
+        })
+        assert env.get('FOOBAR') is None
+
+    def test_get_boolean(self):
+        env = Environment({
+            'FOO': '',
+            'BAR': '0',
+            'BAZ': 'FALSE',
+            'FOOBAR': 'true',
+        })
+
+        assert env.get_boolean('FOO') is False
+        assert env.get_boolean('BAR') is False
+        assert env.get_boolean('BAZ') is False
+        assert env.get_boolean('FOOBAR') is True
+        assert env.get_boolean('UNDEFINED') is False