Configures NTP Servers by default

- Packstack should configure NTP on each nodes
- By default, it will use [0,1,2,3].fedora.pool.ntp.org

Change-Id: Ie593297f036eb2994118d1dc4286d3efa7cd4716
Fixes: rhbz#1086349
Signed-off-by: Gael Chamoulaud <gchamoul@redhat.com>