Don't clobber test exit code at cleanup in LDAP/Kerberors tests
If the test script die()d before running the first test, the whole test
was interpreted as SKIPped rather than failed. The PostgreSQL::Cluster
module got this right.
Backpatch to all supported versions.
Discussion: https://www.postgresql.org/message-id/
fb898a70-3a88-4629-88e9-
f2375020061d@iki.fi