utils: Bail if we fail to truncate lockfile

If we can't truncate it, we're most likely not going to be able to write
our PID to it. Bail early, and let the user know what's going on.

Signed-off-by: Anton Lofgren <alofgren@op5.com>
Merge pull request #75 from catharsis/check-ftruncate-ret

utils: Bail if we fail to truncate lockfile