ipatests: Fixes for test_ipahealthcheck_ipansschainvalidation testcases.
    
    Currently the test is using IPA_NSSDB_PWDFILE_TXT which is /etc/ipa/nssdb/pwdfile.txt
    which causes error in STIG mode.
    
    [root@master slapd-TESTRELM-TEST]# certutil -M -n 'TESTRELM.TEST IPA CA' -t ',,' -d . -f /etc/ipa/nssdb/pwdfile.txt
    Incorrect password/PIN entered.
    
    Hence modified the test to include paths.ETC_DIRSRV_SLAPD_INSTANCE_TEMPLATE/pwd.txt.
    
    Signed-off-by: Sudhir Menon <sumenon@redhat.com>
    Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>