Move {name}-publish-specs job + others to ubuntu-xenial

This commit moves all the specs-jobs to xenial. Previously this job as done
on trusty.

Change-Id: I461edff862e1bcda1d49dfce27efb12790484cbe

jenkins/jobs/specs-jobs.yaml

@@ -2,7 +2,7 @@
 
 - job-template:
     name: '{name}-publish-specs'
-    node: ubuntu-trusty
+    node: ubuntu-xenial
 
     # We want to publish to org/name but the scp publisher cannot remove paths,
     # so use a shell builder to move the content in the right place and publish
@@ -53,7 +53,7 @@
 - job:
     name: gate-generate-specs-site
     description: Render the specs sites templates without publishing them.
-    node: ubuntu-trusty
+    node: ubuntu-xenial
 
     builders:
       - generate-specs-site
@@ -64,7 +64,7 @@
 - job:
     name: publish-specs-site
     description: Render the specs sites templates and publish them.
-    node: ubuntu-trusty
+    node: ubuntu-xenial
 
     builders:
       - generate-specs-site