Fix export syntax compatibility with older sh
seen on Solaris 10:
$ ./run test077
Running ./scripts/test077-sasl-gssapi for mdb...
running defines.sh
Starting KDC for SASL/GSSAPI tests...
./scripts/test077-sasl-gssapi: KRB5_TRACE=/export/home/ryan/openldap/tests/testrun/k5_trace: is not an identifier