Simplify OpenDev push-upstream job

This patch adjust the OpenDev push-upstream jenkins job to follow the
following rules:
* do not change the commit that is being upstreamed
* do not force the git user.name to be the gerrit id. Git authorship can
  be independent from gerrit review ownership. Query Nordix Gerrit about
  the user name instead.
* consider 'no new changes' error from OpenDev Gerrit as success as it
  means the current patch is up-to-date upstream

Change-Id: Ib7a0d9d6052db357148d07f57b141730b837055f