WIP : Add Stretch Support

[roumano]

WIP as tresure data still not provide stretch support :
treasure-data/omnibus-td-agent#107
and the repository is empty for stretch :
https://td-agent-package-browser.herokuapp.com/2/debian/
so this role is failing :

TASK [williamyeh.fluentd : add td-agent repository] ***********************************************************************************
fatal: [stretch]: FAILED! => {"changed": false, "failed": true, "module_stderr": "Shared connection to 127.0.0.1 closed.\r\n", "module_stdout": "sudo: unable to resolve host dockerstretch\r\nTraceback (most recent call last):\r\n  File \"/tmp/user/0/ansible_03ULBR/ansible_module_apt_repository.py\", line 565, in <module>\r\n    main()\r\n  File \"/tmp/user/0/ansible_03ULBR/ansible_module_apt_repository.py\", line 553, in main\r\n    cache.update()\r\n  File \"/usr/lib/python2.7/dist-packages/apt/cache.py\", line 464, in update\r\n    raise FetchFailedException(e)\r\napt.cache.FetchFailedException: E:The repository 'https://packages.treasuredata.com/2/debian/stretch stretch Release' does not have a Release file.\r\n", "msg": "MODULE FAILURE", "rc": 0}