wizard should short-circuit to failure page instead of step 2 if installation is unhealthy

Steps to reproduce:
-Freshly install a node
-Stop the service
-Put these lines in the /etc/security/limits.conf file:

northscale soft nofile 1024
northscale hard nofile 1024

This will cause memcached to crash on startup

-Restart the service
-Connect to the UI to walk through the wizard
-Note that you can't get past the second screen due to:
Your path is invalid. It must be a directory writable by northscale user

The error is not really correct, and it will send the user down an invalid path to resolution.