Fix memory leak in generate_key wrapper. Other fixes.

- catch errors in looking for the keyring
- static_assert to prevent a buffer overrun
- remove obsolete, misleading comment
- dial down priority of some log messages
- explain why we ignore some errors
- idiomatic C++11

Bug: 27552432
Change-Id: Ic3ee05b41eae45e7c6b571a459b326a483663526
3 files changed