Update git submodules

* Update docs/submodules/integration.git from branch 'master'
  to 21b09c956609d3ebee0081686802d20da194c523
  - Improve vCPE test automation
    
    Signed-off-by: Yang Xu <yang.xu@futurewei.com>
    Issue-ID: INT-847
    Change-Id: Ib5b0a547f1c228de4cee02f3526401028c10bff0
    
1 file changed