Update use of heartbeat in agent
Update use of heartbeat in agent

THe TTL argument means something slightly different now.

Also: start heartbeating as soon as possible. There's a race between
the session being established and records being entered. (A more
involved fix would be to _require_ the session to be established
entering records.)

squaremo/ambergreen,squaremo/ambergreen,squaremo/ambergreen,squaremo/ambergreen,squaremo/ambergreen