Add traefik 1.5 formatted logs and update grok rule to handle them

[rhooper]

With traefik 1.5 access logs, the grok rules in the module failed to pars any logs. The updated grok pattern handles these.

[elasticmachine]

Since this is a community submitted pull request, a Jenkins build has not been kicked off automatically. Can an Elastic organization member please verify the contents of this patch and then kick off a build manually?

[andrewkroh]

Jenkins, test it

[ruflin]

This seems to be the same / similar change as in #6136

@e8kor @rhooper Could you collaborate on this one? The part that is important form my side is that we have test files for both cases / versions.

[iwex]

@rhooper any updates?

[sayden]

Fixed in #8768