[9.20] fix: test: Ignore softhsm2 errors when deleting token in keyfromlabel test

In some rare cases, the softhsm2 utility reports failure to delete the
token directory, despite the token being found. Subsequent attempts to
delete the token again indicate that the token was deleted.

Ignore this cleanup error, as it doesn't prevent our tests from working
properly. There is also an attempt to delete the token before the test
starts which ensures a clean state before the test is executed, in case
there's actually a leftover token.

Closes #5244

Backport of MR !10607

Merge branch 'backport-5244-ignore-softhsm2util-delete-token-error-9.20' into 'bind-9.20'

See merge request isc-projects/bind9!10608