Respect new HAVE_CHEF_WEBUI option from crowbar

Do not add a link to the chef webui for that node if there's no webui.
Merge pull request #173 from jdsn/release/pebbles/master-wait-for-pxe

reintroduce wait_for_pxe_state to fix node state transistions with slow admin nodes
Revert "reintroduce wait_for_pxe_state to fix node state transistions"

This reverts commit eff468bbb9658635f4737db7c0cdbdc82999959a
which should not have been merged - see:

  https://github.com/crowbar/barclamp-provisioner/pull/173
Merge pull request #176 from aspiers/revert-essex-hack-suse-wait-for-pxe-state

Revert "reintroduce wait_for_pxe_state to fix node state transistions".

Merging without smoke-test since simply returns repo to previous state.
Merge pull request #174 from vuntz/no-chef-link

Respect new HAVE_CHEF_WEBUI option from crowbar
wait_for_pxe function

in order to prevent a node from getting stuck due to a slow admin
node the node should wait for the proper pxe file to be present
before proceeding