Add packages needed to build lxml

This commit adds the ubuntu packages needed to build lxml which is now
being pulled it because of the addition of rss support to
openstack-health's api server.

Change-Id: Id59c044413f47b59a471fe9a915caf4cca64d253

manifests/api.pp

@@ -55,6 +55,14 @@ class openstack_health::api(
     ensure => present,
   }
 
+  package {'libxml2-dev':
+    ensure => present,
+  }
+
+  package {'libxslt1-dev':
+    ensure => present,
+  }
+
   exec { 'requirements':
     command     => "${virtualenv_dir}/bin/pip install -U -r ${source_dir}/requirements.txt",
     require     => Python::Virtualenv[$virtualenv_dir],