Fix DServer Misc test when not executed from a docker container

Give FQDN instead of simple HOSTNAME when passing the hostname in serverhost and clienthost tests parameters. FQDN is what is expected by the tests, as described in cpp_test_suite/README file:

clienthost --clienthost= client host's fully qualified domain name, e.g. mypc.myinstitute.com (small caps) serverhost --serverhost= fully qualified domain name of the host on which the server is running, e.g. myserver.myinstitute.com (small caps)

This avoids DServer Misc test failure when the test is not executed from a Docker container.