Configure log file for upstart.

[jdavisp3]

This PR configures a log file for the upstart configuration similar to the one for the init.d configuration.

I tested this by provisioning a consul server with the new configuration and observing the log file being created log entries being appended. I restarted the service and the new entries were appended to the existing file.

[solarkennedy]

But if you are running consul as non-root, will it be able to continue to log? I guess it doesn't really log to a file anyway.

[jdavisp3]

Thanks for taking my contribution!

But if you are running consul as non-root, will it be able to continue to log? I guess it doesn't really log to a file anyway.

In my test setup the consul Java process does not run as root but it is able to log to the file. The upstart configuration will create the log file as root and set up the I/O redirection before launching the start-stop-daemon process which switches to the consul user.

Note this configuration does log to a file: /var/log/consul.