Add --dest-bucket to chromite/scripts/pushimage.py

Add flag so that dest bucket can be set to chromeos-throwaway-bucket,
so that we can get new release builders running without actually
modifying our production bucket (chromeos-releases).
Also, Use this flag in the PushImage Build API endpoint.

BUG=chromium:1159569
TEST=run_tests

Cq-Depend: chromium:2599476
Change-Id: I594502a111adc0ba65a4683a9695afcd44c9d93c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2599290
Reviewed-by: George Engelbrecht <engeg@google.com>
Commit-Queue: Jack Neus <jackneus@google.com>
Tested-by: Jack Neus <jackneus@google.com>
diff --git a/api/controller/image_unittest.py b/api/controller/image_unittest.py
index c647e11..6fabccf 100644
--- a/api/controller/image_unittest.py
+++ b/api/controller/image_unittest.py
@@ -415,13 +415,14 @@
 
     request = self._GetRequest(
         dryrun=False, profile='', sign_types=[common_pb2.IMAGE_TYPE_RECOVERY])
+    request.dest_bucket = 'gs://foo'
     image_controller.PushImage(request, self.response, self.api_config)
     patch.assert_called_with(
         request.gs_image_dir,
         request.sysroot.build_target.name,
         dry_run=request.dryrun,
-        profile=request.profile.name,
-        sign_types=['recovery'])
+        sign_types=['recovery'],
+        dest_bucket=request.dest_bucket)
 
   def testCallSucceeds(self):
     """Check that a (dry run) call is made successfully."""