Add default nginx access log pattern

[germaaan]

No description provided.

[elasticsearch-release]

Jenkins standing by to test this. If you aren't a maintainer, you can ignore this comment. Someone with commit access, please review this and clear it for Jenkins to run; then say 'jenkins, test it'.

[wyardley]

I was using the Apache Combined pattern, and seemed to mostly match. Which specific things are you changing (looks like you're using Nginx w/ normal combined log format)?

Not affiliated with elastic, but just curious, where is the NGUSER pattern coming from, since it doesn't seem to be in your changeset?

I was experiencing an issue due to email addresses in the authenticated username field, and submitted a pull request for that here.
#142