Adding ability for keystore to find dropbox

This will allow the logging in keystore to actually work.

Bug: 36549319
Test: keystore dropbox logging is successful
Change-Id: Ic135fa9624c289c54187e946affbd0caacef13c1
(cherry picked from commit 2e69afc079a175070279674be78aacbe4434c367)

public/keystore.te

@@ -13,6 +13,7 @@ allow keystore keystore_exec:file { getattr };
 
 add_service(keystore, keystore_service)
 allow keystore sec_key_att_app_id_provider_service:service_manager find;
+allow keystore dropbox_service:service_manager find;
 
 # Check SELinux permissions.
 selinux_check_access(keystore)