Add driver.docker counter metric for OOM Killer events

Disable Exec on non-linux platforms

This PR disables exec on non-linux platforms

Fix consul server resync when server and client point to the same Consul agent

This commit fixes an issue where if a nomad client and server shared the same consul instance, the server would deregister any services and checks registered by clients for running tasks.

Raw exec can use cgroups to manage PIDs

Add go-discover support to Nomad clients

test fixes

This commit changes the force closing of the stdout/stderr file
descriptor from closing immediately to being closed after a grace
period. This allows the created process to close its own file and allows
copying of the data.