Basic Nexus 2.7 support

Updated attributes for new version
Rewrite the jetty.xml template because it is different in Nexus 2.7
Rewrite the nexus executeable template because it is different in Nexus 2.7
Pass less to the configure Proc
do less manipulation of the actual server
Remove data bag requirements

Add a new attribute for installing a custom SSL certificate
Stop modifying the log endpoint (requires credentials data bag)
improve log message
Merge pull request #57 from RiotGames/nexus_2.7

Support Nexus 2.7