If /mnt/stateful_partition/unencrypted/preserve directory doesn't exist when attestationd needs to write attestaion.epb file, it attempts to create that directory. That fails since mkdir is not allowed by minijail:
2017-03-29T11:31:42.120079-07:00 ERR attestationd[4871]: libminijail[4871]: blocked syscall: mkdir


Note that if the directory doesn't exist when the daemon starts, the upstart script fails since it attempts the following in pre-start:
  chgrp preserve /mnt/stateful_partition/unencrypted/preserve
  chmod 775 /mnt/stateful_partition/unencrypted/preserve

Same thing should be happening with tpm_managerd and /var/lib/tpm_manager/local_tpm_data

It also starts with base::CreateDirectory() when writing to the file.