New expiration keys for operations

[hchac]

toppatch/vFense#32

Use the new expiration keys "server_queue_ttl" and "agent_queue_ttl" in each operation to determine if an operation should be placed in queue and/or processed.

1. With "server_queue_ttl" the agent should determine, by checking if the current epoch time is less than the value of this key, if the operation is worth putting into the agent queue. This serves as a backup to what the server is already doing, by checking if the operation is past its "pickup time," meaning the operation should have not been picked up by the agent due to its expiration.

2. With "agent_queue_ttl" the agent should determine, by checking if the current epoch time is less than the value of this key, if the operation should be processed. This tells the agent to avoid processing operations that have been sitting in queue for too long.