Update git submodules

Update git submodules

* Update docs/submodules/releng from branch 'master'
  to 0837527fbcc32862bbdd22fc1b02f7848da3021f
  - Use a local cache for JJB jobs

    This should prevent the error:

        Traceback (most recent call last):
          File "/tmp/tmp.5aGg6za4Iw/bin/jenkins-jobs", line 8, in <module>
            sys.exit(main())
          File "/tmp/tmp.5aGg6za4Iw/lib/python3.5/site-packages/jenkins_jobs/cli/entry.py", line 165, in main
            jjb.execute()
          File "/tmp/tmp.5aGg6za4Iw/lib/python3.5/site-packages/jenkins_jobs/cli/entry.py", line 146, in execute
            ext.obj.execute(self.options, self.jjb_config)
          File "/tmp/tmp.5aGg6za4Iw/lib/python3.5/site-packages/jenkins_jobs/cli/subcommand/test.py", line 55, in execute
            options, jjb_config)
          File "/tmp/tmp.5aGg6za4Iw/lib/python3.5/site-packages/jenkins_jobs/cli/subcommand/update.py", line 97, in _generate_xmljobs
            builder = JenkinsManager(jjb_config)
          File "/tmp/tmp.5aGg6za4Iw/lib/python3.5/site-packages/jenkins_jobs/builder.py", line 60, in __init__
            flush=jjb_config.builder['flush_cache'])
          File "/tmp/tmp.5aGg6za4Iw/lib/python3.5/site-packages/jenkins_jobs/cache.py", line 54, in __init__
            "Unable to lock cache for '%s'" % jenkins_url)

    Change-Id: Ia027d64aec0caf582893009e709f938531bea15d
    Signed-off-by: Trevor Bramwell <tbramwell@linuxfoundation.org>