handle multiple NTP servers (bnc#895824)

sntp seems to use only the first NTP server and ignore others
https://bugzilla.novell.com/show_bug.cgi?id=895824

cherry picked from commit 16c242f356414d1c6427e027cc34d8b096eabfc1
Conflicts:
	chef/cookbooks/provisioner/templates/default/crowbar_join.suse.sh.erb