Test: Add test cases for NTP
Test: Add test cases for NTP

Resolves openbmc/openbmc#2106

Change-Id: I93bbbb1178dc47fa94f98719185630020e00edda
Signed-off-by: Ratan Gupta <a42a43504c26cfe5294e3d72712325cd74a43440@in.ibm.com>

openbmc/phosphor-networkd,openbmc/phosphor-networkd