Temporarily disable com.android.cts.cpptools.RunAsHostTest#testRunAs

Change-Id: I7121a29cfd93347ed62156ff2d6c8c10d7a66b4d
diff --git a/tests/expectations/knownfailures.txt b/tests/expectations/knownfailures.txt
index a6b8f87..19360e9 100644
--- a/tests/expectations/knownfailures.txt
+++ b/tests/expectations/knownfailures.txt
@@ -374,5 +374,10 @@
       "android.security.cts.MediaCryptoTest#testMediaCryptoWidevine"
   ],
   bug: 27218502
+},
+{
+  description: "Still investigating this, root cause unknown yet",
+  bug: 27578806,
+  names: ["com.android.cts.cpptools.RunAsHostTest#testRunAs"]
 }
 ]