Improve the generation of the jruby facet by inspecting the .ruby-version file and generating an appropriate rbenv environment

git-svn-id: https://svn.apache.org/repos/asf/buildr/trunk@1525840 13f79535-47bb-0310-9956-ffa450edef68
Ensure that the web facet picks other vendor specific deployment descriptors if present

git-svn-id: https://svn.apache.org/repos/asf/buildr/trunk@1525842 13f79535-47bb-0310-9956-ffa450edef68