[Telemetry] Disable power.idle_platform on failing android platforms.

They are failing because of a clock sync issue where a clock sync path between
ftrace and telemetry cannot be found.

Bug: 773949
Change-Id: I4823387051b644fd198bf619abc6205d628f89fd
Reviewed-on: https://chromium-review.googlesource.com/716559
Reviewed-by: Ned Nguyen <nednguyen@google.com>
Commit-Queue: rnephew <rnephew@chromium.org>
Cr-Commit-Position: refs/heads/master@{#508459}

tools/perf/benchmarks/power.py

@@ -80,5 +80,9 @@ def Name(cls):
   def GetExpectations(self):
     class StoryExpectations(story.expectations.StoryExpectations):
       def SetExpectations(self):
-        pass # Nothing disabled.
+        self.DisableBenchmark(
+            [story.expectations.ANDROID_NEXUS5,
+             story.expectations.ANDROID_NEXUS6,
+             story.expectations.ANDROID_NEXUS7,
+             story.expectations.ANDROID_ONE], 'crbug.com/773949')
     return StoryExpectations()