Selinux: Policies for otapreopt_chroot and postinstall_dexopt

Give mount & chroot permissions to otapreopt_chroot related to
postinstall.

Add postinstall_dexopt for otapreopt in the B partition. Allow
the things installd can do for dexopt. Give a few more rights
to dex2oat for postinstall files.

Allow postinstall files to call the system server.

Bug: 25612095
Change-Id: If7407473d50c9414668ff6ef869c2aadd14264e7
diff --git a/file_contexts b/file_contexts
index b3e4e93..75edcc9 100644
--- a/file_contexts
+++ b/file_contexts
@@ -174,7 +174,7 @@
 /system/bin/mediacodec	u:object_r:mediacodec_exec:s0
 /system/bin/mdnsd	u:object_r:mdnsd_exec:s0
 /system/bin/installd	u:object_r:installd_exec:s0
-/system/bin/otapreopt   u:object_r:otapreopt_exec:s0
+/system/bin/otapreopt_chroot   u:object_r:otapreopt_chroot_exec:s0
 /system/bin/keystore	u:object_r:keystore_exec:s0
 /system/bin/fingerprintd u:object_r:fingerprintd_exec:s0
 /system/bin/gatekeeperd u:object_r:gatekeeperd_exec:s0