Added Console Logging to HaaS

This patch adds console logging to HaaS by running ipmitool subprocesses that
log to files.  There is now an API call 'show_console' that displays the
contents of the console log to the user.  Log files are securely deleted when
nodes have a change in ownership.
*This* would be a good thing to wrap up in a helper method on the node. look at `Headnode._vmname()` for a reference.