deals partially with #1973

see also https://github.com/vjeantet/grok/issues/17

fixes #1810

this log format is likely soon going to be removed from a future
influxdb release, so we should not be recommending that users base any
of their log parsing infra on this.

closes #1436

This also fixes the bad behavior of waiting until runtime to return log
parsing pattern compile errors when a pattern was simply unfound.

closes #1418

Also protect against user error when the telegraf user does not have
permission to open the provided file. We will now error and exit in this
case, rather than silently waiting to get permission to open it.

closes #1479

closes #1434

closes #102
closes #328