Drop attribute 'root' from bc-template-provisioner.json

It was only used in recipes/update_nodes.rb whereas recipes/base.rb used
a node[:platform] check to set the correct tftpboot path. This would
all to drop a hack in SUSE packages.
Merge pull request #150 from saschpe/release/pebbles/master-drop-root-attr

Drop attribute 'root' from bc-template-provisioner.json