Since it takes time for the agent to get the response and set the
cookie and, as well, the time into a request that a LoadBalancer is
initialized varies by many seconds (cookies loaded from the start),
give the cookie a much lower TTL than the DB positions in the stash.
This avoids having to wait for a position with a given cpPosIndex
value, when the position already expired from the store, which is
a waste of time.
Also include the timestamp in "cpPosIndex" cookies to implement
logical expiration in case clients do not expire them correctly.
Bug: T194403
Bug: T190082
Change-Id: I97d8f108dec59c5ccead66432a097cda8ef4a178
52af356cad