Update git submodules
Update git submodules

* Update plugins/download-commands from branch 'master'
  to edd715618415d9a5e03b4555d9a2d3cca8fff6e8
  - Merge branch 'stable-2.15'
    
    * stable-2.15:
      Support an extra command for ssh command
    
    Change-Id: If2f68f9c83dae2faf038718d9ec94ba31587e330
    
  - Support an extra command for ssh command
    
    This would be useful to add an extra command like initializing submodules.
    
    Change-Id: If418279493e8556a8176a8b828c5edfc9f88e997
    
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