Merge #14409: utils and libraries: Make 'blocksdir' always net specific

e4a0c3547e Improve blocksdir functional test. (Hennadii Stepanov)
c3f1821ac7 Make blockdir always net specific (Hennadii Stepanov)

Pull request description:

  The blocks directory is net specific by definition.

  Also this prevents the side effect of calling `GetBlocksDir(false)` in the non-mainnet environment.
  Currently a new node creates an unused `blocks\` directory in the root of the data directory when `-testnet` or `-regtest` is specified.

  Refs:
  - #12653
  - https://github.com/bitcoin/bitcoin/pull/12653#discussion_r174784834 by @laanwj
  - https://github.com/bitcoin/bitcoin/issues/14595#issuecomment-436011186

Tree-SHA512: c9957a68a4a200ebd2010823a56db7e61563afedcb7c9828e86b13f3af2990e07854b622c1f3374756f94574acb3ea32de7d2a399eef6c0623f0e11265155627

test/functional/feature_blocksdir.py

@@ -18,6 +18,8 @@ class BlocksdirTest(BitcoinTestFramework):
 
     def run_test(self):
         self.stop_node(0)
+        assert os.path.isdir(os.path.join(self.nodes[0].datadir, "regtest", "blocks"))
+        assert not os.path.isdir(os.path.join(self.nodes[0].datadir, "blocks"))
         shutil.rmtree(self.nodes[0].datadir)
         initialize_datadir(self.options.tmpdir, 0)
         self.log.info("Starting with nonexistent blocksdir ...")