Fix plugins if building standalone Mercury

# Mercury

if [[ ( "${DEPENDENCY}" == "" ) || ( "${DEPENDENCY}" == "mercury" ) ]]; then

    if [ "$NA_LAYER" == "bmi" ] || [ "$NA_LAYER" == "all" ]; then

        USE_BMI="-DNA_USE_BMI:BOOL=ON"

    fi

    if [ "$NA_LAYER" == "ofi" ] || [ "$NA_LAYER" == "all" ]; then

        USE_OFI="-DNA_USE_OFI:BOOL=ON"

    fi

    echo "############################################################ Installing:  Mercury"

    CURR=${SOURCE}/mercury

    prepare_build_dir ${CURR}