JDK-8232153: pass NSS option for certificate test
Changes:
- d/t/jtreg-autopkgtest.{sh,in}: JDK-8232153 - set NSS_DEFAULT_DB_TYPE to let sun/security/pkcs11/Secmod/AddTrustedCert.java pass.
 
Testing:
- Test passes in bionic chroot.
 
Edited  by Vladimir Petko