Parsing seat_id on bid response for BidSwitch

[sandiemann]

There is a docker env variable with "BIDSWITCH_ID" as a seat id for the exchange but the env variable is not parsed correctly on running bidder instance. It results in "localhostSWITCH_ID" because there is another env variable $BID with default value as "localhost".
The solution would be to rename the "BIDSWITCH_ID" variable name to avoid value mapping conflicts.