Plan/Engine: Set plan_id before dispatching pcs when starting new plan

[oysstu]

The call to changeMode dispatches a PlanControlState message with state initializing, but does not set the new plan_id. This sets the plan_id before the call to changeMode when starting a new plan to avoid dispatching a PlanControlState message with the name of the previous plan and initializing. See the attached Neptus screenshot where the plan test2 is started during the execution of test1.

[oysstu]

Added another commit that also sets the plan_eta and plan_progress variables to -1.