Remove useless chef-client execution

chef-client is already executed after a reboot. There's no need to
trigger the run again.
Simplify conditional check
Improve reboot done check

Use the requested reboot time stored before a reboot to verify that
a reboot is done.
Check node state after reboot

When node is back after a reboot, a chef-client run is triggered by
crowbar_join. Wait until the chef-client run finished and check that
the node gets back to "ready" state to be sure that the whole reboot was
successful.
Merge pull request #1095 from toabctl/reboot-handler-cleanup

Reboot handler cleanup
Fix several links to nodes

nodes_path(:selected => @node.handle) now doesn't work anymore,
node_path(@node.handle) is the new way.
Remove support for selected paramater to node index page

It doesn't do anything anymore already.
Fix saving of target platform

Don't only save the target platform on allocation: we want to save on
save before allocation too.
Fix nodes not displaying any target platform

When prettrifying the target platform, we were not using our internal
method that falls back to the default platform, resulting in the pages
showing nothing at all as target platform.
Merge pull request #1097 from vuntz/node-path

Fix several links to nodes
Merge pull request #1098 from vuntz/target-platform

Fixes related to saving and displaying the target platform