NEXUS-5563: Scrape and HTTP

Scrape should kick in only on HTTP/HTTPS repositories.
This is critical, as it's not only procurement that
might interfere here, but also a plugin contributed
alternate RRS implementation, as one might add
FTP or BWP (brain-wave-protocol) powered RRS
implementations too from a plugin.
NEXUS-5563: UT for non-HTTP url case

The fact that repo is a proxy does not means it might be
a HTTP/HTTPS only proxy.