entrypoint.sh: export MIRROR_CONF for use by go test code

Later changes to the test Go code will make use of the MIRROR_CONF
variable to access the secondary ceph cluster.

Signed-off-by: John Mulligan <jmulligan@redhat.com>

entrypoint.sh

@@ -259,6 +259,7 @@ test_go_ceph() {
     fi
     if [[ ${MIRROR_CONF} && ${CEPH_VERSION} != nautilus ]]; then
         setup_mirroring
+        export MIRROR_CONF
     fi
     for pkg in "${pkgs[@]}"; do
         test_pkg "${pkg}" || test_failed "${pkg}"