add option to use multiple defaults sections

[vicinus]

If there is interest in this feature I will add documentation and spec tests. The patch add the option to use multiple defaults section, as described in the haproxy documentation:

A "defaults" section sets default parameters for all other sections following
its declaration. Those default parameters are reset by the next "defaults"
section. See below for the list of parameters which can be set in a "defaults"
section. The name is optional but its use is encouraged for better readability.

It's completely optional. Additionally if defaults are used, then the frontend and backend section are kept together in the haproxy configuration file if the frontend has the option default_backend or the frontend and backend are identical named. We are using multiple defaults and the improved ordering to improve the readability in our very long haproxy configuration files.

[bmjen]

@vicinus This is a good start and extension of the haproxy module. And as far as I can tell, it maintains backwards compatibility as well. I'd be on board with moving forward with docs and tests.

/cc @hunner for 2nd opinion

[vicinus]

I have added documentation, spec tests and acceptance tests. Please let me know if documentation or spec tests needs to be expanded further.

Also as far as I can tell, the failed checks are not caused due to my changes. One issue is that haproxy::params::merge_options is used as a default value in haproxy::instance without inheriting haproxy::params.

[jonnytdevops]

@bmjen Does this look good to you now? I managed to re-run the travis/docker build and got it passing.