graphics: TraceReplayExtended: use new PowerTest.* vars prefix

This sets up the controlling graphics_TraceReplayExtended server test
to conform to the new prefix convention for tast vars: "PowerTest.*".

BUG=b:185822218
TEST=test_that -b hatch --fast \
     $DUT graphics_TraceReplayExtended.glxgears_1minute

Cq-Depend: chromium:2868179, chrome-internal:3804048
Change-Id: I5cd1bfabb84235bc12be19d5bdf2192aab0ad81f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/autotest/+/2872494
Tested-by: Ryan Neph <ryanneph@google.com>
Reviewed-by: Po-Hsien Wang <pwang@chromium.org>
Reviewed-by: Ilja H. Friedel <ihf@chromium.org>
Commit-Queue: Ryan Neph <ryanneph@google.com>
diff --git a/server/site_tests/graphics_TraceReplayExtended/graphics_TraceReplayExtended.py b/server/site_tests/graphics_TraceReplayExtended/graphics_TraceReplayExtended.py
index c9cc425..e467fa1 100644
--- a/server/site_tests/graphics_TraceReplayExtended/graphics_TraceReplayExtended.py
+++ b/server/site_tests/graphics_TraceReplayExtended/graphics_TraceReplayExtended.py
@@ -229,11 +229,9 @@
         if not tast_varslist:
             tast_varslist = []
         tast_varslist.extend([
-            'graphics.TraceReplayExtended.resultDir=' + result_dir,
-            'graphics.TraceReplayExtended.signalRunningFile=' +
-            signal_running_file,
-            'graphics.TraceReplayExtended.signalCheckpointFile=' +
-            signal_checkpoint_file,
+            'PowerTest.resultDir=' + result_dir,
+            'PowerTest.signalRunningFile=' + signal_running_file,
+            'PowerTest.signalCheckpointFile=' + signal_checkpoint_file,
         ])
 
         tast_instance = tast.tast(