Improve logging of certificate auto-renew
After #3251 (closed) is implemented we have cron jobs running to renew the certificate.
However, the output of cron task leaves a lot to be desired for:
2018-04-12_13:34:40.66619 go-crond: Starting go-crond version 0.6.1
2018-04-12_13:34:40.66674 go-crond: Add cron job spec:'22 0 */4 * *' usr:root cmd:'/opt/gitlab/bin/gitlab-ctl renew-le-certs'
2018-04-12_13:34:40.66682 go-crond: Start runner with 1 jobsThat is pretty much it. We don't have any trace that the job is actually being executed. Having no logs will make it impossible to debug problems and verify that the things are operational. We should either increase the verbosity of what the cron service is doing or add additional redirects to logs within the command that is being run.