Don't crash if there is no crowbar proposal

For some reason in my installation currently proposals[0]
is nil.
Use /var/run/crowbar for locking instead of /tmp

Using predictable filenames in /tmp for locking is not secure.
Cleanup looper_chef_client.sh

Always touch the chef-client.run file first, and use a variable for
this path.
suse: Remove lock files used by chef-client wrappers on start
suse: Make init script create /var/run/crowbar
Merge pull request #676 from dirkmueller/release/pebbles/master

Don't crash if there is no crowbar proposal
Merge pull request #706 from vuntz/fix-chef-client-calls

Use /var/run/crowbar for locking instead of /tmp [1/2]
Removing stale TODO and updating ISO link