do not set created span as current span

[pdincau]

With @mbusi we noticed that we are currently setting as current span the span we create when the http request is issued, this forces us to store the original span and probably leads to incorrect behaviour when the http call fails for nxdomain.

A different approach could consist in storing the created span instead of the parent, not setting the span as current and then ending the stored span as:

Span.end_span(stored_span)