Add a test to check for IXFR->AXFR race-condition

Add a test to check for IXFR->AXFR race-condition

The test initiates a zone transfer with IXFR, which produces
a big amount of differences and then generates an error. The
secondary should be able to gracefully shutdown the ongoing
IXFR transfer and retry with AXFR without race conditions
between them.

This test checks for an issue (GL#5767) but since a race
condition is usually time-sensitive it might require several
attempts before it reproduces the issue.

(cherry picked from commit 5c248e7d1acb97468d304d0e44f0074c5fbfc750)