Consul validate should accept -config-format flag

[snocorp]

Description of the Issue (and unexpected/desired result)

We are using ansible to build our consul configuration and we would like to be able to validate our configration during the template generation phase. Ansible creates a temporary file without an extension to be the file that gets tested. Unfortunately this means the config file will be skipped and the validation will fail. While looking into this issue I noticed that when running the agent, one can override the format using the -config-format flag but this flag is not accepted in the validate command.

The expected result would be if I specify the format, it will override or choose the format (hcl|json) using that flag instead of only using the file extension.

Reproduction steps

$ consul validate -config-format json consul.conf
flag provided but not defined: -config-format

consul version for both Client and Server

Client: 1.0.6
Server: 1.0.6

consul info for both Client and Server

n/a

Operating system and Environment details

Ubuntu 16.04.3

Log Fragments or Link to gist

n/a