Undertow access_log prefix/suffix default values discrepancy

Schema definition of Undertow access log prefix and suffix attributes in this file do not match what is in access log definition - see the difference in
access_log -> access_log. and .log -> log

There was a change in this commit.

Those values should match and according to mentioned commit I propose to edit schema definition to what is in access log definition file (therefore: prefix = "access_log." and suffix = "log").

NOTE: I am setting target for GA as this is trivial change in schema definition and better to change it before GA as after this any change to schema definition is difficult.