Add aliveness testing and hooks for node lifecycle events. [1/1]

This pull request adds support in CB 2.0 for oppourtunistic aliveness testing, and adds hooks and basic infrastructure for roles to be aware of node creation and destruction.

Currently, aliveness testing will happen every time a jig wants to run on a node -- if the node is marked as alive, we will ping it with one ping and then SSH into it to run a simple command.  If either the ping or the SSH fail, the node is marked as not alive and the jig will do nothing.

 crowbar_framework/app/models/node.rb      |   25 +++++++++++++++++++++++++
 crowbar_framework/app/models/node_role.rb |    1 +
 crowbar_framework/app/models/role.rb      |    9 +++++++++
 3 files changed, 35 insertions(+)

Crowbar-Pull-ID: 2798298cf4060cce4c5c1e9267da5cce0e27fe3c

Crowbar-Release: development