After discussing this in the QE team, we believe that this error message
2016-07-21 05:33:00,363 ERROR [org.wildfly.extension.undertow] (MSC service thread 1-2) WFLYUT0071: Jetty ALPN not found. HTTP2 and SPDY are not available. Please make sure Jetty ALPN is on the boot class path.
should be demoted to WARN to not cause too much panic with every server start.
Also, maybe we could enhance it to contain some instructions how to explicitly disable HTTP/2 in order to get rid of this message completely?