Adjust symlink for nova-compute logs on metal

Current symlink isn't mounted on the rsyslog container because its a symlink.
Reversing the symlink will work for rsyslog.

* Create the log directory in /openstack/log with appropriate permissions
* Link to this directory from /var/log/nova
* Adjust the directory to include the physical node name

Fixes #87
Merge pull request #88 from andymcc/compute_log_fix

Adjust symlink for nova-compute logs on metal