webconnectivity@v0.5: do not attempt to use bogons

[bassosimone]

In measurements #1, #2 and #3, we say there is TCP/IP blocking because we fail to TCP connect. In both cases, we're connecting to a bogon and to a valid address and both fail. The point of this issue is that it is not even worth attempting to use the bogon, because once we see it we know something is very wrong. Additionally, as pointed out by @fortuna, it is unwise to fetch content from bogons, because their meaning changes from network to network.

[koderrr]

Would be nice to fix this, it will speed up the web connectivity test.
For example, on my network most of the blocked sites resolve to 172.22.0.249, and for every address it's wasting time for TCP connect check and HTTP GET check, 30 seconds in total.

778 blocked websites amounted to 6.5 hours wasted.