Fix cf-execd sending too many emails.

Timestamps in the log file would make all cf-agent logs look different
so cf-execd would send an email on every run, even if nothing changed.
Fixed by removing the timestamps before comparing each log line.

Fixes issue 3011.
(cherry picked from commit 0f6c0d697e0766271eef7669c45a16dc3e1bd7d4)
Update ChangeLog with fix for #3011