Selinux: introduce policy for OTA preopt

Add permissions to dex2oat, introduce otapreopt binary and otadexopt
service.

Bug: 25612095
Change-Id: I80fcba2785e80b2931d7d82bb07474f6cd0099f7
diff --git a/service_contexts b/service_contexts
index 1f3e572..747369e 100644
--- a/service_contexts
+++ b/service_contexts
@@ -84,6 +84,7 @@
 network_score                             u:object_r:network_score_service:s0
 nfc                                       u:object_r:nfc_service:s0
 notification                              u:object_r:notification_service:s0
+otadexopt                                 u:object_r:otadexopt_service:s0
 package                                   u:object_r:package_service:s0
 permission                                u:object_r:permission_service:s0
 persistent_data_block                     u:object_r:persistent_data_block_service:s0