Update Undertow version

Gives a slight speed boost due to path handler improvements
Don't use snapshot netty version

This at least allows the test to run. This is not the most
recent version of netty as it appears the API changed between CR and final.
Don't use MediaType.toString()

The result is not cached and it is really slow (according to yjp about 13%
of CPU time).
Merge pull request #386 from stuartwdouglas/master

Update Undertow version and use non-snapshot version of netty