Disable HTTP connection pooling
Disable HTTP connection pooling by asking HTTP server to close our
connection right upon use. The rationale is that some BMC observed in
the wild seem to close persistent connections abruptly upon eventual
re-use failing completely unrelated operation. So in ``sushy`` we
just try not to maintain persistent connections with BMC at all.
(cherry picked from commit 84e085f9a2460218bf52315a21ee4dcf8365e3e1)