Create flexible NTP server list for nailgun
Create flexible NTP server list for nailgun

NTP server list should be comma separated and
support 0-3 servers without any trailing commas.

Change-Id: Ic1566f2bf7da4401e152287dd879c4184612acd4
Closes-Bug: #1452665

eayunstack/fuel-library,ddepaoli3/fuel-library-dev,huntxu/fuel-library,eayunstack/fuel-library,ddepaoli3/fuel-library-dev,huntxu/fuel-library,xarses/fuel-library,ddepaoli3/fuel-library-dev,stackforge/fuel-library,ddepaoli3/fuel-library-dev,eayunstack/fuel-library,xarses/fuel-library,stackforge/fuel-library,stackforge/fuel-library,eayunstack/fuel-library,eayunstack/fuel-library,stackforge/fuel-library,xarses/fuel-library,xarses/fuel-library,ddepaoli3/fuel-library-dev,huntxu/fuel-library,huntxu/fuel-library,huntxu/fuel-library