api/controller: Convert manual BuildTarget instantiations

There are controller_util functions to construct BuildTargets from
the protobuf messages so we can have a single place to address changes
to the protobuf message. Convert all the BuildTarget instantiations
from manual constructions to calls to the util function.

BUG=chromium:1060351
TEST=run_tests, cq

Change-Id: I60c6720cf7bbc60f122f2fa1e2e81ab13368193f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2096818
Reviewed-by: Michael Mortensen <mmortensen@google.com>
Commit-Queue: Alex Klein <saklein@chromium.org>
Tested-by: Alex Klein <saklein@chromium.org>
diff --git a/api/controller/packages_unittest.py b/api/controller/packages_unittest.py
index 70b9542..297fba0 100644
--- a/api/controller/packages_unittest.py
+++ b/api/controller/packages_unittest.py
@@ -21,7 +21,7 @@
 from chromite.lib import cros_build_lib
 from chromite.lib import cros_test_lib
 from chromite.lib import portage_util
-from chromite.lib.build_target_lib import BuildTarget
+from chromite.lib import build_target_lib
 from chromite.service import packages as packages_service
 
 
@@ -555,7 +555,8 @@
     request = self._GetRequest(board='foo')
     packages_controller.BuildsChrome(request, self.response, self.api_config)
     self.assertTrue(self.response.builds_chrome)
-    patch.assert_called_once_with(constants.CHROME_CP, BuildTarget('foo'), [])
+    patch.assert_called_once_with(constants.CHROME_CP,
+                                  build_target_lib.BuildTarget('foo'), [])
 
   def testBuildsChromeWithPackages(self):
     """Test successful call with packages handling."""
@@ -569,5 +570,6 @@
     request = self._GetRequest(board='foo', packages=[package])
     packages_controller.BuildsChrome(request, self.response, self.api_config)
     self.assertTrue(self.response.builds_chrome)
-    patch.assert_called_once_with(constants.CHROME_CP, BuildTarget('foo'),
+    patch.assert_called_once_with(constants.CHROME_CP,
+                                  build_target_lib.BuildTarget('foo'),
                                   [controller_util.PackageInfoToCPV(package)])