HTTP headers 'Host:' and 'User-Agent:' fixed

### Description
The HTTP headers 'Host' and 'User-Agent' were truncated.
That is now fixed and the corresponding functional tests have been modified accordingly.
The version of libcurl has been added to the user-agent.

This PR is related to the issue #442.
I made those fixes in another branch yesterday, I guess I can erase it now :+1: 

*NTC*