test: update test-run

* Support to set default SQL engine using _session_settings space in
  addition to pragma sql_default_engine. This feature is only for
  *.test.sql tests. Needed for #4511.

* Use exact IPv4/IPv6 address in test_run:cmd() in order to avoid rare
  failures due to using wrong address (PR #197).

(cherry picked from commit a6535ab3b8d3e395d2f81699cf35329118412307)