I suppose that node 4 got ext-4 fs error when we erased it during processing new deployment operation. Cobbler successfully rebooted node-4, but if mbr alive, we got error (boot order for system test: hd, netboot).  I can not say more without real env which we could not restore (

This bug remember me about useful patchset: https://review.openstack.org/#/c/108188/ (5.1, but for 5.0.x it can be big change).

Stop deploy:
2014-07-22T03:25:15 debug: [402] MCO final result: mco success nodes: [{"uid"=>"1"}, {"uid"=>"2"}, {"uid"=>"4"}], mco error nodes: [], mco inaccessible nodes: [], all mco nodes: [{"uid"=>"2"}, {"uid"=>"4"}, {"uid"=>"1"}]

Deploy after:
2014-07-22T03:32:37 warning: [400] : Removing of nodes ["1", "2", "3", "4", "5"] finished with errors. Nodes [{"uid"=>"4", "error"=>"Node not answered by RPC."}] are inaccessible.

Cobbler:

2014-07-22T03:32:39 debug: [400] Cobbler syncing
2014-07-22T03:32:40 debug: [400] Trying to reboot node: node-1
2014-07-22T03:32:40 debug: [400] Trying to reboot node: node-2
2014-07-22T03:32:40 debug: [400] Trying to reboot node: node-3
2014-07-22T03:32:40 debug: [400] Trying to reboot node: node-4
2014-07-22T03:32:40 debug: [400] Trying to reboot node: node-5
2014-07-22T03:32:40 debug: [400] Cobbler syncing
2014-07-22T03:32:41 debug: [400] Waiting for reboot to be complete: nodes: ["node-1", "node-2", "node-3", "node-4", "node-5"]
2014-07-22T03:32:41 debug: [400] Reboot task status: node: node-1 status: [1405999960.464637, "Power management (reboot)", "running", []]
2014-07-22T03:32:42 debug: [400] Reboot task status: node: node-2 status: [1405999960.464637, "Power management (reboot)", "running", []]
2014-07-22T03:32:42 debug: [400] Reboot task status: node: node-3 status: [1405999960.464637, "Power management (reboot)", "running", []]
2014-07-22T03:32:42 debug: [400] Reboot task status: node: node-4 status: [1405999960.464637, "Power management (reboot)", "running", []]
2014-07-22T03:32:42 debug: [400] Reboot task status: node: node-5 status: [1405999960.464637, "Power management (reboot)", "running", []]
2014-07-22T03:32:47 debug: [400] Reboot task status: node: node-1 status: [1405999960.464637, "Power management (reboot)", "running", []]
2014-07-22T03:32:47 debug: [400] Reboot task status: node: node-2 status: [1405999960.464637, "Power management (reboot)", "running", []]
2014-07-22T03:32:47 debug: [400] Reboot task status: node: node-3 status: [1405999960.464637, "Power management (reboot)", "running", []]
2014-07-22T03:32:47 debug: [400] Reboot task status: node: node-4 status: [1405999960.464637, "Power management (reboot)", "running", []]
2014-07-22T03:32:47 debug: [400] Reboot task status: node: node-5 status: [1405999960.464637, "Power management (reboot)", "running", []]
2014-07-22T03:32:52 debug: [400] Reboot task status: node: node-1 status: [1405999960.464637, "Power management (reboot)", "complete", []]
2014-07-22T03:32:52 debug: [400] Successfully rebooted: node-1
2014-07-22T03:32:52 debug: [400] Reboot task status: node: node-2 status: [1405999960.464637, "Power management (reboot)", "complete", []]
2014-07-22T03:32:52 debug: [400] Successfully rebooted: node-2
2014-07-22T03:32:52 debug: [400] Reboot task status: node: node-3 status: [1405999960.464637, "Power management (reboot)", "complete", []]
2014-07-22T03:32:52 debug: [400] Successfully rebooted: node-3
2014-07-22T03:32:52 debug: [400] Reboot task status: node: node-4 status: [1405999960.464637, "Power management (reboot)", "complete", []]
2014-07-22T03:32:52 debug: [400] Successfully rebooted: node-4
2014-07-22T03:32:52 debug: [400] Reboot task status: node: node-5 status: [1405999960.464637, "Power management (reboot)", "complete", []]
2014-07-22T03:32:52 debug: [400] Successfully rebooted: node-5
2014-07-22T03:32:57 info: [400] Starting OS provisioning for nodes: 1,2,3,4,5