Elastic IP isn't associated if one already exists

In order to maintain cross compatibility between openstack and AWS,
an EIP was anyway being attached to the instance.

This patch fixes it.

Signed-off-by: Shashank Sahni <shredder12@gmail.com>
Running multistack-cdh4 cookbook

Using multistack-cdh4 recipe as default now. The CDH4 repo provides
most software in Hadoop ecosystem pre-packaged. Hence, shifting to
it.

Signed-off-by: Shashank Sahni <shredder12@gmail.com>