qa: repair the rpc-test harness so it can start a DragonX node at all

The integration suite has never run against DragonX. Six independent
defects stacked up, each only visible once the previous was fixed:

1. test_framework used python2 implicit relative imports
   ("from authproxy import ..."), removed in python3, so every test died
   at import. Made explicit relative imports.

2. It wrote ZZZ.conf -- a Komodo assetchain convention -- while DragonX
   reads DRAGONX.conf. The daemon therefore never saw the generated
   config, fell back to mainnet defaults and tried to bind RPC 21769,
   which on a seed node is already held by the real node.

3. start_node() was hard-wired for the -ac_name=ZZZ assetchain tests: it
   took the RPC port from extra_args[3], passed extra_args[0] as argv[0]
   of the CLI, and only wrote a config when extra_args[0] matched. Any
   test that passes no extra args crashed on len(None). The generic path
   now takes the port from rpc_port(i) -- the same helper
   initialize_datadir() already used -- and drives the CLI with -datadir.

4. dragonxd refuses to start without an asmap file, which no test datadir
   had. initialize_datadir() now provisions one.

5. -asmap relative paths resolve against the NET-SPECIFIC datadir, so a
   copy in <datadir> is never found. Pass an absolute path.

6. Worst: -regtest was only ever set as "regtest=1" in the conf file,
   which DragonX ignores. Every "regtest" node therefore ran on MAINNET:
   real genesis, real seeds, real peers. An observed run synced 196,180
   live blocks and 679MB into /tmp before the test timed out. -regtest is
   now passed as a command-line flag, with -connect=0 so an isolated
   regtest node stays off the public network.

With these, nodes start, RPC answers, and tests run to a real result.
They do not all pass yet -- getblocktemplate.py reaches an assertion --
but that is now a test outcome rather than a harness failure.

qa/rpc-tests/test_framework/comptool.py

@@ -3,10 +3,10 @@
 # Distributed under the GPLv3 software license, see the accompanying
 # file COPYING or https://www.gnu.org/licenses/gpl-3.0.en.html
 
-from mininode import CBlock, CTransaction, CInv, NodeConn, NodeConnCB, \
+from .mininode import CBlock, CTransaction, CInv, NodeConn, NodeConnCB, \
     msg_inv, msg_getheaders, msg_ping, msg_mempool, mininode_lock, MAX_INV_SZ
-from blockstore import BlockStore, TxStore
-from util import p2p_port
+from .blockstore import BlockStore, TxStore
+from .util import p2p_port
 
 import time