Force logwrapper to system_file

Some device-specific policies are improperly creating a security
domain for logwrapper, rather than removing the logwrapper
lines from init.device.rc. Don't allow that. Explicitly add an entry
for /system/bin/logwrapper to force it to a system_file. Attempting
to override this will result in the following compile time error:

  obj/ETC/file_contexts_intermediates/file_contexts: Multiple different
  specifications for /system/bin/logwrapper
  (u:object_r:logwrapper_exec:s0 and u:object_r:system_file:s0).

Bug: 15616899
Change-Id: Ia55394247a9fa16e00434d61091fff9d9d4ff125