Handle fatal errors in ExchangeClient

Treat certain errors in the HttpPageBufferClient as fatal and abort the
ExchangeClient rather than retrying forever.
Add failed request count for HttpPageBufferClient
Shorten ExchangeClientConfig method names
Fail queries after too many ExchangeClient errors

A query will fail if errors continue for longer than the minimum duration.
Add configuration option for exchange max response size
Remove unnecessary downcast in AbstractVariableWidthRandomAccessBlock