cheets_GTS.py: Support run 'all' command

Now cheets_GTS.py will run the entire GTS suite when no target_package is
specified.

BUG=b:36464569
TEST=run `android-gts/tools/gts-tradefed run commandAndExit gts` on my workstation

Change-Id: I9a855421f5e2e8bff2cbf4ad1b1d18242e250629
Reviewed-on: https://chromium-review.googlesource.com/553439
Commit-Ready: Ilja H. Friedel <ihf@chromium.org>
Tested-by: Ilja H. Friedel <ihf@chromium.org>
Reviewed-by: Ilja H. Friedel <ihf@chromium.org>
diff --git a/server/site_tests/cheets_GTS/cheets_GTS.py b/server/site_tests/cheets_GTS/cheets_GTS.py
index fb138d3..ea06986 100644
--- a/server/site_tests/cheets_GTS/cheets_GTS.py
+++ b/server/site_tests/cheets_GTS/cheets_GTS.py
@@ -25,6 +25,7 @@
 class cheets_GTS(tradefed_test.TradefedTest):
     """Sets up tradefed to run GTS tests."""
     version = 1
+    _target_package = None
 
 
     def setup(self, uri=None):
@@ -41,14 +42,12 @@
         self.waivers = self._get_expected_failures('expectations')
 
 
-    def _get_gts_test_args(self, target_package):
-        """ This is the command to run GTS tests.
-
-        @param target_package: the name of test package to be run. If None is
-                set, full GTS set will run.
-        """
-        self._target_package = target_package
-        return ['run', 'commandAndExit', 'gts', '--module', target_package]
+    def _get_gts_test_args(self):
+        """ This is the command to run GTS tests."""
+        args = ['run', 'commandAndExit', 'gts']
+        if self._target_package is not None:
+            args += ['--module', self._target_package]
+        return args
 
 
     def _run_gts_tradefed(self, gts_tradefed_args):
@@ -100,9 +99,13 @@
         logging.info('The test has passed successfully.')
 
     def run_once(self, target_package=None, gts_tradefed_args=None):
-        """Runs GTS target package exactly once."""
+        """Runs GTS target package exactly once.
+        @param target_package: the name of test package to be run. If None is
+                               set, full GTS set will run.
+        """
+        self._target_package = target_package
         with self._login_chrome():
             self._ready_arc()
             if not gts_tradefed_args:
-                gts_tradefed_args = self._get_gts_test_args(target_package)
+                gts_tradefed_args = self._get_gts_test_args()
             self._run_gts_tradefed(gts_tradefed_args)