add docs for error provisioner
add docs for error provisioner

paulmey/packer,paulmey/packer,mitchellh/packer,rnaveiras/packer,timsutton/packer,mitchellh/packer,dave2/packer,mitchellh/packer,timsutton/packer,paulmey/packer,ricardclau/packer,dave2/packer,paulmey/packer,hashicorp/packer,mitchellh/packer,hashicorp/packer,mitchellh/packer,ricardclau/packer,ricardclau/packer,timsutton/packer,ricardclau/packer,pecigonzalo/packer,grubernaut/packer,grubernaut/packer,pecigonzalo/packer,dave2/packer,dave2/packer,dave2/packer,rnaveiras/packer,timsutton/packer,timsutton/packer,grubernaut/packer,rnaveiras/packer,pecigonzalo/packer,rnaveiras/packer,ricardclau/packer,pecigonzalo/packer,timsutton/packer,hashicorp/packer,hashicorp/packer,grubernaut/packer,grubernaut/packer,rnaveiras/packer,dave2/packer,ricardclau/packer,grubernaut/packer,paulmey/packer,paulmey/packer,rnaveiras/packer