Fail/Errorout the execution on runtime

fail function was used to fail if memcached service was not registered with
consul. But the problem there was, the memcached was started on the same nodes
as nova controllers which caused a situation where puppet never executed as fail
function run on compile time and it did not get a chance to setup memcached.

Added a type to error the puppet execution and thus any dependant resource to
that wont be running.

Added runtime_fail type to nova controller and made a dependancy to nova_config where
memcache is configured.