change buffer size to 8 MiB in buffered_reader

Link: https://github.com/GeneAssembly/biosal/issues/466
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
fix code that test requests

Link: https://github.com/GeneAssembly/biosal/issues/456
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
set concrete transport object too

Link: https://github.com/GeneAssembly/biosal/issues/468
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>