Mongo 3.4 and (partial) Xenial support

[vesse]

This pull request would:

• Add MongoDB 3.4 support with configurable signing_key
• Use ansible_distribution_release in APT sources, or fallback to the previously hard-coded values

MongoDB Xenial repositories now provide the needed systemd unit at least for 3.2 and 3.4 so there's no need to build one manually.

The service in Ansible system module seems to enable the systemd service and start it properly when run on real server, but when running Ubuntu 16.04 in Docker the setup fails with no service or tool found for: mongod which is probably because Ansible shows upstart in ansible_service_mgr when run on image built from Ubuntu official 16.04 base image.

I did deploy a working MongoDB 3.4 on Xenial with the currently release version with this in my group_vars:

mongodb_version: "3.4.1"
mongodb_repository_config:
  v3.4:
    repository: deb http://repo.mongodb.org/apt/ubuntu xenial/mongodb-org/3.4 multiverse
    package: mongodb-org
mongodb_version_config:
  v3.4:
    daemon: mongod
    config_file: mongod.conf

which is what this pull request should produce.

mongodb_transparent_hugepage_disable does not work with this pull request on systemd because it creates an upstart file and I didn't do anything to it. And as mentioned there's a Docker problem, hopefully you have better insight in it than I do.

[pigulla]

Any chance of this getting merged?

[wangsha]

+1

[pigulla]

Paging @klen

[JMLX42]

I would like to see this merged too plz.