tpm_manager: generate human-readable owner passwords

As it is done in cryptohome for TPM1.2, generate human-readable
owner passwords by producing a hexdump of random bytes.

BUG=chrome-os-partner:62698
TEST=During OOBE, click on "System security settings" in EULA
     dialogue. Verify that, once TPM is owned, the displayed
     password is 20 characters from '0..9A..F' set.

Change-Id: I979826f86bfb98c97bf03ed1d5082da976b85fbe
Reviewed-on: https://chromium-review.googlesource.com/440412
Commit-Ready: Andrey Pronin <apronin@chromium.org>
Tested-by: Andrey Pronin <apronin@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>
3 files changed