cros_run_tast_vm_test: Pass -extrauseflags=tast_vm.

Make cros_run_tast_vm_test pass -extrauseflags=tast_vm to
the "tast run" command. This will be used to skip tests that
require features that are only provided by real hardware.

BUG=chromium:885016
TEST=betty-release-tryjob passed -extrauseflags=tast_vm

Change-Id: Ib6a93d4198368abe2e266d2fe3b3276b4f92d1c5
Reviewed-on: https://chromium-review.googlesource.com/1258126
Commit-Ready: Dan Erat <derat@chromium.org>
Tested-by: Dan Erat <derat@chromium.org>
Reviewed-by: Achuith Bhandarkar <achuith@chromium.org>
diff --git a/cros_run_tast_vm_test b/cros_run_tast_vm_test
index 8bddf61..fdc4e74 100755
--- a/cros_run_tast_vm_test
+++ b/cros_run_tast_vm_test
@@ -53,6 +53,10 @@
   run_args+=("-keyfile=${chroot_key}")
 fi
 
+# Inject a "tast_vm" USE flag to be used when computing dependencies.
+# This makes it possible to skip tests that require real hardware.
+run_args+=("-extrauseflags=tast_vm")
+
 trap stop_kvm EXIT
 start_kvm "${FLAGS_image_path}" "${FLAGS_board}"
 retry_until_ssh