Allow adbd to pull sepolicy from device.

Address the following denial when running CTS:
avc: denied { search } for comm=73657276696365203136 name="/" dev="selinuxfs" ino=1 scontext=u:r:adbd:s0 tcontext=u:object_r:selinuxfs:s0 tclass=dir permissive=0

Bug: 26290097
Change-Id: Icf51061a65a5fda15f7e7ef78200a62ffbd1ca9b

adbd.te

@@ -86,6 +86,9 @@ allow adbd appdomain:unix_stream_socket connectto;
 allow adbd zygote_exec:file r_file_perms;
 allow adbd system_file:file r_file_perms;
 
+# Allow pulling the SELinux policy for CTS purposes
+allow adbd selinuxfs:dir r_dir_perms;
+allow adbd selinuxfs:file r_file_perms;
 allow adbd kernel:security read_policy;
 
 allow adbd surfaceflinger_service:service_manager find;