NEXUS-5472: Added dead simple throttling

Just a sleep, that slows down scrape. In case of Central
the change is from 3min to 5min scrape time change, by adding
200ms sleep time between index page fetches.
Nexus Core client fix.

Seems it was neglecting some important values from Nexus Status.
Merge remote-tracking branch 'origin/master' into nexus-5472-proxy404
Introduced Nexus Core Testsuite

A new module that will contain Nexus Core ITs, but
in contrast to "legacy" nexus-test-harness-its module,
these ITs are the mew one, written using the new IT
infrastructure plus the client, instead of the old
stuff.