services/mgmt/device/impl/app_service.go: Create app STDERR/STDOUT w/ mode 644

Create STDERR/STDOUT files for apps with world-readable permissions by default,
to match what is already happening with INFO logs, and to allow the logs to
be readable remotely when in multi-user mode. These permissions should still
be subject to the umask of devmgr in case someone wants stricter access control

Change-Id: I8c2d3573fb72bdfc0f089e27c49b9aa78a1d8877
1 file changed