open log file in append mode so log file isn't truncated
open log file in append mode so log file isn't truncated

jab1982/opennsa,jab1982/opennsa,NORDUnet/opennsa,jeroenh/OpenNSA,jeroenh/OpenNSA,jeroenh/OpenNSA,NORDUnet/opennsa,NORDUnet/opennsa