fix disk failure step 1 - happy path, fix by cloning template node

for each node with failed disks, it will be fixed with step 1 powerOff node, step 2:
createReplacementVm, step 3: a chef bootstrap step on the bad node.

Changes include:
1. implement clusterHealService to fix cluster errors, start from disk failure
2. implement disk failure handling job and according steps
3. record system disk in table disk. It's a plus besides the data and swap disk
4. update CreateVmSp to attach existed vmdks, only create and add disks that don't
  have vmdk path
create empty vm is system disk is good
Merge branch 'fixdisk'
try destroy first then unregister it when failed
Merge branch 'master' of github.com:vmware-serengeti/serengeti-ws