Separated out GetRandomizedDNSSeeds into its own files. Over time, these new files can house the
DNS seed related logic and constants that currently reside in the net.h/cpp mess.

• Rename DNSSeeds -> GetRandomizedDNSSeeds
• Make the currently node-specific randomization logic available to the seeder
• Doing the above also incidentally makes better use of the vector copy that I introduced in this patch.

Tests still failing.

abc_mining_basic.py still needs to test that the old prefix is valid for mining

• Fixed checking if the arg is set
• Added another sanity checking test case

The cppcheck issue appears to be a bug in cppcheck. Fabien has confirmed this lint error does not appear in a newer version.

• Refactor and simplify the logic tracking checkpoint state
• Refactor and simplify the tests
• Rewrite summary and test plan
• New changes depend on D8673 to make the test plan easier to understand by simple examination of the command line arguments in each step.

Looks like we need some better test coverage to make sure bitcoin-qt in server mode work as expected.

Rebase and add some basic test coverage

@bot build-linux32 build-osx

@bot build-linux32 build-osx

This was a good question. There's multiple copies going on here and they aren't necessary.
While the handling of the outgoing data stream is not identical between the seeder and the
node software, the new WriteMessage function can easily write directly to the stream in
question instead of copying into an intermediate which then is copied into the outgoing stream.

• Improve the API for testing
• Use NetMsgType::GETADDR in place of a hardcoded string
• Other minor nits

• Rebase ontop of linker fixes: D8622
• Use netmagic from config instead of hardcoding the values in multiple places. (More cleanup can be done here, but out of scope of this patch)
• Use TransportSerializer.prepareForTransport to de-dup header serialization code.

There's an ava functional test, so at least original behavior still works as expected. Not much more to test here.

Functional test would be ideal. Manual test instructions in the test plan at minimum though. Both would be best :)

Fix clang build

Moved function to generated file and fixed test failure