Validate config file before deploying

[kasimon]

Use validate_cmd to check the config file for validity before actually installing it.

[solarkennedy]

Hmm. This seems like a good idea. It does imply that the consul binary is installed and ready to go. Seems legit.

[kasimon]

Yes, the binary has to be present, but it does not have to be set up in any way. The validation happens independently from the normal service setup.

Thanks for merging!

[wyardley]

I know there is a compatibility matrix in the README, but this does break consul on versions where the version doesn't yet support consul validate. Maybe there should be a conditional based on consul version?

Also, I think this breaks the default config? The module default in params.pp seems to be 0.7.4 (https://github.com/solarkennedy/puppet-consul/blob/master/manifests/params.pp#L44), even though the readme says current is >= 0.8.0. So either default should be updated to 0.8.5 (or 1.x), or the validation should be skipped when the version doesn't support it.