doth: RNDC reconfiguration too slow on OpenIndiana

Even with 2e5f9a0d RNDC reconfiguration in doth system test takes 30-60 second and dig invocations fail with "connection refused" on OpenIndiana (but not on Solaris 11.4). Affects doth tests "checking DoT query after a reconfiguration" and "checking DoH query (POST) after a reconfiguration".

Keep nameds from doth system test running and issue ../../../bin/rndc/rndc -c common/rndc.conf -p 5312 -s 10.53.0.4 reconfig command:

...
11-Jan-2022 16:43:49.938 calling free_rbtdb(.)
11-Jan-2022 16:43:49.938 done free_rbtdb(.)

Only after 30 seconds (sometimes close to 60 seconds) named is ready:

11-Jan-2022 16:44:19.082 listening on IPv4 interface lo0, 10.53.0.4#5301
11-Jan-2022 16:44:19.083 listening on IPv4 interface lo0, 10.53.0.4#5303

Otherwise, ../../../bin/dig/dig +tls +noadd +nosea +nostat +noquest +nocmd -p 5301 @10.53.0.4 example SOA fails with:

;; Connection to 10.53.0.4#5301(10.53.0.4) for example failed: connection refused.
;; Connection to 10.53.0.4#5301(10.53.0.4) for example failed: connection refused.
;; Connection to 10.53.0.4#5301(10.53.0.4) for example failed: connection refused.

CPU utilization of named looks sub 1% during the reconfiguration.