NPMImpl does not use cloud provider to rertieve nodes anymore

Previously, the NodesRegistry was only a cache structure,
but now it holds the nodes managed by the NPM.
The idea is that NPM manages only know the nodes created by it,
otherwise it could try to use a VM that I created to other purposes.
This change leads to a more controlled environment.
Merge branch 'master' of https://github.com/choreos/choreos_middleware
Node creation extracted to the NodeCreator class

CloudProvider interface changed to not use the jclouds exception.
AWSCloudProvider test change since the last verification of the test did not test anything actully.

A little hack was also inserted at NPMImpl to make FixedCloudProvider work!
NodeRegistry must be not changed by NodeCreator
NPMImpl test
changes in NodeSelector interface
configure log on FixedConnectionTest