Add --device-build flag to build_test_suites.py

The flag will be used to differentiate device builds so we can do the appropriate BWYN logic. Also include DIST_DIR as a required env var.

Bug: 378704055
Change-Id: I203645ab82d52024a713c41c6fdc806f8672f7cc
Test: atest build_test_suites_test
diff --git a/ci/build_test_suites_test.py b/ci/build_test_suites_test.py
index 26f4316..503a5f4 100644
--- a/ci/build_test_suites_test.py
+++ b/ci/build_test_suites_test.py
@@ -78,6 +78,12 @@
     with self.assert_raises_word(build_test_suites.Error, 'TOP'):
       build_test_suites.main([])
 
+  def test_missing_dist_dir_env_var_raises(self):
+    del os.environ['DIST_DIR']
+
+    with self.assert_raises_word(build_test_suites.Error, 'DIST_DIR'):
+      build_test_suites.main([])
+
   def test_invalid_arg_raises(self):
     invalid_args = ['--invalid_arg']
 
@@ -121,6 +127,7 @@
         'TARGET_RELEASE': 'release',
         'TARGET_PRODUCT': 'product',
         'TOP': str(self.fake_top),
+        'DIST_DIR': str(self.fake_top.joinpath('dist')),
     })
 
     self.mock_subprocess_run.return_value = 0