Random read if marginally read ahead was seen to improve perf for a TPCH query.
Introducing fs.azure.readahead.range parameter which can be set by user.
Data will be populated in buffer for random reads as well which leads to lesser
This patch also changes the seek implementation to perform a lazy seek. Actual
seek is done when a read is initiated and data is not present in buffer else
date is returned from buffer thus reducing the number of remote calls.