Do not remove from LB if not yet added

[ssalinas]

In this order of events, we were submitting a LB ADD request after the REMOVE request, with the result that the presence of the REMOVE caused us to never properly remove the task from the LB:

• deploy 1 running
• deploy 2 starts
• replacement task for deploy 1 enters TASK_RUNNING
• deploy 2 tasks are healthy and LB ADD/REMOVE is triggered (but contains the replacement task above)
• replacement task from deploy 1 becomes healthy and LB ADD is sent

This fixes the deploy logic to only issue the REMOVE as part of the deploy if the ADD is already present and successful. If the ADD completes after/during the deploy lb actions, the task will still be properly removed from the LB during cleanup since the LB REMOVE will not be present.

[ssalinas]

This tested well in each of our environments, merging the fix