Rename two 'users' variables to make then clearer

'users_dotfiles_enabled_default' becomes 'users_default_dotfiles'.
'users_default_dotfile' becomes 'users_default_dotfiles_key'.
Add delay for network interface restart

'interfaces' role will wait 2 seconds between stopping and starting
a network interface to let other sybsystems catch up.
Add more Ubuntu releases in 'apt_preferences'
Change default MySQL bind address to 'localhost'
Remove options not needed in interface config

Seems that ifupdown correctly manages bridge interfaces without manual
brctl commands required.
Fix container state management in 'lxc' role

For some reason, 'awk' command on Ubuntu returns multiple values of
a string instead of a single one. To mitigate that, we can use
'stdout_lines[0]' instead of 'stdout' key to check for correct LXC
container state.
Fix a typo in a comment, add more information
Make 'monit' default variable file more readable
Replace 'ansible_managed' with a static comment

'ansible_managed' variable in templates was causing Ansible to rewrite
the template despite the fact that configuration haven't changed. This
rewrite triggered a "changed" status, which notified some handlers,
which were needlessly restarted. All that caused repeaded playbook runs
to be not idempotent, longer and could distrupt services for some time.

This patch replaces 'ansible_managed' variable in all templates with
a short static comment which indicates that the file is managed by
Ansible and all changes made to it will be lost.
Update CHANGELOG.md
Merge pull request #156 from drybjed/bugfixes

Many bugfixes in various roles