tlsdated: log more aggressively

Sometimes it's not clear from syslogs when tlsdated is starting and exiting, so
make it be explicit about these things when verbose. Also, dump both the cached
timestamp and the sysclock at startup.

Signed-off-by: Elly Fong-Jones <ellyjones@chromium.org>
Merge pull request #82 from elly/aggressive-logging

tlsdated: log more aggressively