Newer Consul version available shouldn't be an error

[jameshartig]

Overview of the Issue

The Newer Consul version available log doesn't need to be an error. It should be a informational message or warning at most. We typically act/alert on error messages and have hundreds of servers firing this.

Reproduction Steps

N/A

Consul info for both Client and Server

N/A

Operating system and Environment details

CentOS 7 on GCE

Log Fragments

[ERROR] agent: Newer Consul version available: new_version=1.7.2 current_version=1.7.1