Change the "enabled" label for SetLowPriorityForBeacon

This is needed to start the experiment on beta.

Bug: 1018081
Change-Id: I753809054a6f4d5119401ddc79439dcd3ca60713
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1902173
Auto-Submit: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#713993}

testing/variations/fieldtrial_testing_config.json

@@ -5724,7 +5724,7 @@
             ],
             "experiments": [
                 {
-                    "name": "Enabled",
+                    "name": "Enabled_20191107",
                     "enable_features": [
                         "SetLowPriorityForBeacon"
                     ]