crowbar_join.suse: Remember reboot request

Remember reboot request so crowbar can wait until the reboot finished.
This is done in crowbars run_remote_chef_client() function. The newly added
start handler resets the reboot state.

https://bugzilla.novell.com/show_bug.cgi?id=878012
Merge pull request #320 from toabctl/remember-reboot

crowbar_join.suse: Remember reboot request