Add proccess monitor to keepalived

Add proccess monitor to keepalived

Adding process monitor to keepalived code, so that keepalived processes
launched by the L3 agent will get monitored the same as other processes
launched by the L3 agent.

Old monitoring code was removed since it's not needed anymore.

Implements: blueprint agent-child-processes-status

Change-Id: I94a889ee07286ab3c6cdab9ab15e5aee6fbd133a