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.py b/ci/build_test_suites.py
index 623d256..19f0a2c 100644
--- a/ci/build_test_suites.py
+++ b/ci/build_test_suites.py
@@ -30,7 +30,7 @@
 import test_discovery_agent
 
 
-REQUIRED_ENV_VARS = frozenset(['TARGET_PRODUCT', 'TARGET_RELEASE', 'TOP'])
+REQUIRED_ENV_VARS = frozenset(['TARGET_PRODUCT', 'TARGET_RELEASE', 'TOP', 'DIST_DIR'])
 SOONG_UI_EXE_REL_PATH = 'build/soong/soong_ui.bash'
 LOG_PATH = 'logs/build_test_suites.log'
 
@@ -197,6 +197,11 @@
   argparser.add_argument(
       'extra_targets', nargs='*', help='Extra test suites to build.'
   )
+  argparser.add_argument(
+      '--device-build',
+      action='store_true',
+      help='Flag to indicate running a device build.',
+  )
 
   return argparser.parse_args(argv)