Read HTTP response in temp buffer: Fix issue #59

Now reads of the response is done in temp buffer to avoid mixing request and
response
First part of the work for #60 (+ finalize #59)

 - Change the way to manage disconnects while sending a request or receiving a
response.
 - Now Only retry once in case of disconnect

The only unadressed part of #59 was the return status of the operation. For
simplicity, either the response could be fully retrieved, and we return the
length of the reponse; or it couldn't and we return the last error code
(whichever it is).

Thus we will consider that this patch completes the fix to issue #59.
Fix playground server code mistakes
Second part of #60

 - Now, the putrange and getrange properly call a retry-wrapper on top of the
network IO functions.
 - The wrapper supports sglist and buffer functions for maintenance purposes
 - The xfer_scl function within srb_driver.c now only times the call to the
getrange and purange cdmi functions

Should we add the retry mechanism to other calls of the driver (the ones that
are more admin operations) ?
Remove the BIO_ENABLED dead code, Fixes issue #47