Use default ruby packages for Xenial

In I4a5a8352388de46e9e7713fa11951fcde27eaad9 Debian was added as
exception to use default ruby for jenkins::slave. The non-default
ruby1.9.1 also does not exist on Xenial. So add Xenial to the exception
list.

Some alternatives that should be considered:

* Use default ruby packages by default, and add exceptions for distros
where default ruby breaks things. But that can lead to regressions.

* Allow overriding all the default parameters by inheriting from
params.pp, e.g. I8accb1442c6e8a9f1cec5b195d08e96a9b47a9bd.  Which would
make it easier to reuse puppet-jenkins outside of OpenStack infra.

Change-Id: Icac1dafc31b6b2c30860bafe09ca631ff00dd0b1

manifests/params.pp

@@ -51,7 +51,7 @@ class jenkins::params {
       ]
       # ruby packages
       # ruby1.9.1 is not present in Debian Jessie, use ruby instead
-      if ($::operatingsystem == 'Debian') {
+      if ($::operatingsystem == 'Debian' or $::lsbdistcodename == 'xenial') {
         $ruby_package = 'ruby'
         $ruby_dev_package = 'ruby-dev'
       }