use versioncmp to compare versions

[jfroche]

Using builtin function to compare versions in the watch define (https://docs.puppetlabs.com/references/latest/function.html#versioncmp)
I had to rewrite the related tests as well as they were always testing on the '0.4.1' consul::version. I used mocking on hiera to specify the needed version.
Thank you for taking care of this nice module !

[solarkennedy]

Hmm. I'm not a super fan of the hiera mocks, mostly because I've been burned by the "one hiera mock per describe block"

You seem to get around that with with some extra spec help magic.... that I might steal... cc @mrtyler.

Another way you could have done this is with let(:pre_condition){} That would require a tad less magic, maybe. Its all good.

But, I'm going to merge this because it is super! And of course versioncmp, duh.