pushimage: add support for signing accessories images

'accessory_usbpd' and 'accessory_rwsig' are used to sign standalone
accesory MCU firmwares (right now, the former are all the USB type-C
accessories: e.g. Zinger power supply, DingDong and HoHo display
dongles, the latter is the Smaug wireless keyboard).

Signed-off-by: Vincent Palatin <vpalatin@chromium.org>

BUG=chrome-os-partner:46635
TEST=bin/pushimage --debug --test-sign premp --sign-types accessory_rwsig --board smaug gs://chromeos-image-archive/smaug-firmware/R45-7132.239.0
TEST=./scripts/pushimage_unittest

Change-Id: I6481c68061f50b9acc3656a1167d64ced79ec011
Reviewed-on: https://chromium-review.googlesource.com/308725
Commit-Ready: Vincent Palatin <vpalatin@chromium.org>
Tested-by: Vincent Palatin <vpalatin@chromium.org>
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>
diff --git a/scripts/pushimage_unittest.py b/scripts/pushimage_unittest.py
index ae6f6c8..9f5dcf1 100644
--- a/scripts/pushimage_unittest.py
+++ b/scripts/pushimage_unittest.py
@@ -233,7 +233,7 @@
     with mock.patch.object(gs.GSContext, 'Exists', return_value=True):
       urls = pushimage.PushImage('/src', 'test.board', 'R34-5126.0.0',
                                  sign_types=['recovery'])
-    self.assertEqual(self.gs_mock.call_count, 22)
+    self.assertEqual(self.gs_mock.call_count, 26)
     self.assertTrue(self.mark_mock.called)
     self.assertEqual(urls, EXPECTED)
 
@@ -251,7 +251,7 @@
     with mock.patch.object(gs.GSContext, 'Exists', return_value=True):
       urls = pushimage.PushImage('/src', 'test.board', 'R34-5126.0.0',
                                  sign_types=['base'])
-    self.assertEqual(self.gs_mock.call_count, 24)
+    self.assertEqual(self.gs_mock.call_count, 28)
     self.assertTrue(self.mark_mock.called)
     self.assertEqual(urls, EXPECTED)
 
@@ -259,7 +259,7 @@
     """Verify nothing is signed when we request an unavailable type"""
     urls = pushimage.PushImage('/src', 'test.board', 'R34-5126.0.0',
                                sign_types=['nononononono'])
-    self.assertEqual(self.gs_mock.call_count, 20)
+    self.assertEqual(self.gs_mock.call_count, 24)
     self.assertFalse(self.mark_mock.called)
     self.assertEqual(urls, {})