Rspec tests (and fixes)

I just finished a bit of a personal project - rspec tests for this module!

I didn't have much experience with rspec when I started so these are certainly not perfect but they give very good coverage over the module's functionality and config file output. They're modelled on the puppetlabs/apache specs.

The first commit has tests for the current v0.0.6 version of the module, and the subsequent commits contain various isolated fixes for issues I found. I can provide more detail in each commit's description if required, but none will have any effect on current users other than squashing bugs (this is verified by the tests!) except changing the template test for `ipv6_enable` to a boolean check instead of checking a string (if people are setting this to `'false'` instead of `false` for example the behaviour for them will change - having said that the module is now working according to the inline documentation at https://github.com/jfryman/puppet-nginx/blob/master/manifests/resource/vhost.pp#L16).

Anyway I appreciate any and all feedback and hope this gets merged, and that it helps to maintain the quality of the module going forward.

Resolves #65 
Fixes #186