build_packages: Call the sysroot service instead of the shell script

In scripts/build_packages.py, call sysroot.BuildPackages() and
pass along args.
In service/sysroot.py, update BuildPackages to call the shell
script directly and pass along the special chromite flag so
that there aren't deprecation warnings in the build log. Move
construction of the run_config to the caller (build API).

BUG=b:218519852, b:220197678
TEST=manual (`build_packages ...`), CQ

Change-Id: Ied2ff5193ea4852f855e60ed2448efe18e0086c7
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/3448993
Reviewed-by: Ram Chandrasekar <rchandrasekar@google.com>
Tested-by: Cindy Lin <xcl@google.com>
Commit-Queue: Cindy Lin <xcl@google.com>
diff --git a/api/controller/sysroot_unittest.py b/api/controller/sysroot_unittest.py
index 906bf24..fa549dc 100644
--- a/api/controller/sysroot_unittest.py
+++ b/api/controller/sysroot_unittest.py
@@ -608,6 +608,9 @@
                                             self.api_config)
     self.assertFalse(rc)
     rc_patch.assert_called_with(
+        accept_licenses='@CHROMEOS',
+        upgrade_chroot=False,
+        use_any_chrome=False,
         usepkg=True,
         install_debug_symbols=True,
         packages=[],