Move keystore to foreground cpuset.

Bug: 24949295
Change-Id: Iaade68c5216d0efabdfdec4ff2b61d778d319324
diff --git a/keystore/keystore.rc b/keystore/keystore.rc
index a887594..5dac937 100644
--- a/keystore/keystore.rc
+++ b/keystore/keystore.rc
@@ -2,3 +2,4 @@
     class main
     user keystore
     group keystore drmrpc readproc
+    writepid /dev/cpuset/foreground/tasks