App: Adapted PingApp to send pings only between start and stop and when the node is up.

Added test cases for all combinations of node startup/shutdown and ping app start/stop sequences.
App: Adapted IPvXTrafGen to Lifecycle operations.
App: Adapter EtherAppCli and EtherTrafGen to lifecycle operations.
App: Adapted DHCP to Lifecycle operations.
Test: Added a few simple positive lifecycle operation tests for StandardHost.
NodeStatus: Changed to allow specifying initial status in lowercase.
Fixed issues when node is initially down.
todo, split