Introduce check to test if dhclient is running

There have been cases with machines being network configured via dhcp
and not statically. The reason for those was either human error or
misconfiguration of autoinstall. However, these situations were never
caught and would cause outages under certain conditions.  Introducing
this check to catch exactly that

Change-Id: I04f10ff7839c38714db8f3828973d017ceab86a9