tast: Flag flip to enable full remote fixtures

This is a big change. It enables full remote fixtures.
With this flag flip, Tast now runs tests recursively. i.e. remote bundle
invokes local bundle, instead of tast CLI to invoke both remote bundle
and local bundle.
If anything is broken by this change, the change can be locally
reverted by setting TAST_TEST_RECURSIVELY=0 as an environment variable.

BUG=b:187957164
TEST=./fast_build.sh -T

Cq-Depend: chromium:3651846
Disallow-Recycled-Builds: amd64-generic-cq, betty-pi-arc-cq, novato-cq, reven-vmtest-cq
Change-Id: Ib57d961be2b9515b4f3e210df3fab34525f544b8
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/tast/+/3443320
Commit-Queue: Keigo Oka <oka@chromium.org>
Reviewed-by: Kshitij Pancholi <panchok@google.com>
Tested-by: Keigo Oka <oka@chromium.org>
Reviewed-by: Seewai Fu <seewaifu@google.com>
diff --git a/src/chromiumos/tast/cmd/tast/internal/run/driver/run_tests.go b/src/chromiumos/tast/cmd/tast/internal/run/driver/run_tests.go
index 9a1f513..adecab6 100644
--- a/src/chromiumos/tast/cmd/tast/internal/run/driver/run_tests.go
+++ b/src/chromiumos/tast/cmd/tast/internal/run/driver/run_tests.go
@@ -28,14 +28,15 @@
 	"chromiumos/tast/internal/run/resultsjson"
 )
 
-// TestRecursively is environment variable key which is set to "1" to enable
+// TestRecursively is environment variable key which is set to "0" to disable
 // recursive test running flow and support full remote fixtures.
+// TODO(b/187957164): Remove this after migration has finished.
 const TestRecursively = "TAST_TEST_RECURSIVELY"
 
 // ShouldRunTestsRecursively indicates if Tast tests should be run recursively
 // (i.e. remote bundle invokes local bundle).
 func ShouldRunTestsRecursively() bool {
-	return os.Getenv(TestRecursively) == "1"
+	return os.Getenv(TestRecursively) != "0"
 }
 
 // runTestsArgs holds arguments common to private methods called by RunTests.