Add two nbdkit cases

[mxie91]

No description provided.

[mxie91]

avocado run --vt-type v2v nbdkit.plugin.file.fd_fddir

JOB ID : ef8a53f3e5bdc1a886dd2026d26fe1e76fa86c70
JOB LOG : /var/lib/avocado/job-results/job-2023-06-30T11.45-ef8a53f/job.log
(1/1) type_specific.io-github-autotest-libvirt.nbdkit.plugin.file.fd_fddir: STARTED
(1/1) type_specific.io-github-autotest-libvirt.nbdkit.plugin.file.fd_fddir: PASS (96.57 s)
RESULTS : PASS 1 | ERROR 0 | FAIL 0 | SKIP 0 | WARN 0 | INTERRUPT 0 | CANCEL 0
JOB HTML : /var/lib/avocado/job-results/job-2023-06-30T11.45-ef8a53f/results.html
JOB TIME : 99.25 s

avocado run --vt-type v2v nbdkit.check_assertion_failure

JOB ID : 95e471306e8f57ffe7872354e57e3994e4d0fb15
JOB LOG : /var/lib/avocado/job-results/job-2023-06-30T11.49-95e4713/job.log
(1/1) type_specific.io-github-autotest-libvirt.nbdkit.check_assertion_failure: STARTED
(1/1) type_specific.io-github-autotest-libvirt.nbdkit.check_assertion_failure: PASS (94.33 s)
RESULTS : PASS 1 | ERROR 0 | FAIL 0 | SKIP 0 | WARN 0 | INTERRUPT 0 | CANCEL 0
JOB HTML : /var/lib/avocado/job-results/job-2023-06-30T11.49-95e4713/results.html
JOB TIME : 102.57 s

[mxie91]

@xiaodwan pls help to review, thanks!