Upgrade Vaprobash to Ubuntu 16.04 LTS

[Repox]

This pull request specifically targets the upgrade of Ubuntu from 14.04 to 16.04.

Here are some key topics that this upgrade has impact on, which is important to users for this version:

• Docker has been changes to Docker CE
• MongoDB has been updated to versions 3.2 and 3.4 (2.6 had EOL in 2016, 3.0 is troublesome)
• Updated repository and version (to 9.6) for PostgreSQL
• MySQL versions has been bumped to 5.6 and 5.7. 5.5 is no longer available

To test this branch, please make a checkout of this branch (to reflect the version changes in the Vagrantfile) and change your configuration in the Vagrantfile to the following:

# Config Github Settings
github_username = "Repox"
github_repo     = "Vaprobash"
github_branch   = "feature/ubuntu-16.04"
github_url      = "https://raw.githubusercontent.com/#{github_username}/#{github_repo}/#{github_branch}"

I'd appreciate any feedback if you have trouble with the builds.