You should get that GitHub repository and build RPMs from the source. And, only then you'd be able to install it in your CentOS. At least, that's what it tries to explain in the documentation I think. Here(Note: I've changed BUILD_TYPE to Release, so I created Release dir. GIT_VERSION and GIT_COMMIT are not latest ones.):
git clone https://github.com/telefonicaid/fiware-IoTAgent-Cplusplus.git
cd fiware....
mkdir -p build/Release
cd build/Release
cmake -DGIT_VERSION=20527 -DGIT_COMMIT=217023407f25ed258043cfc00a46b6c05fb0b52c -DMQTT=ON -DCMAKE_BUILD_TYPE=Release ../../
make install
make package
The packages should be in pack/Linux/RPM/
rpm -i iot-agent-base-xxxxxxx (xxxxxxx will be the numbers of the build)
rpm -i iot-agent-ul-xxxxxx (xxxxxxx will be the numbers of the build)
After being installed with RPMs, the init.d file must be in: /usr/local/iot/init.d/iotagent
And, this is how the contents of that file would be like:
#!/bin/bash
# Copyright 2015 Telefonica Investigación y Desarrollo, S.A.U
# 
# This file is part of fiware-IoTagent-Cplusplus (FI-WARE project).
# 
# iotagent         Start/Stop iotagent
#
# chkconfig: 2345 99 60
# description: iotagent
. /etc/rc.d/init.d/functions
PARAM=$1
INSTANCE=$2
USERNAME=iotagent
EXECUTABLE=/usr/local/iot/bin/iotagent
CONFIG_PATH=/usr/local/iot/config
iotagent_start()
{
    local result=0
    local instance=${1}
    if [[ ! -x ${EXECUTABLE} ]]; then
        printf "%s\n" "Fail - missing ${EXECUTABLE} executable"
        exit 1
    fi
    if [[ -z ${instance} ]]; then
        list_instances="${CONFIG_PATH}/iotagent_*.conf"
    else
        list_instances="${CONFIG_PATH}/iotagent_${instance}.conf"
    fi
    for instance_config in ${list_instances}
    do
        local NAME
        NAME=${instance_config%.conf}
        NAME=${NAME#*iotagent_}
        source ${instance_config}
        local IOTAGENT_PID_FILE="/var/run/iot/iotagent_${NAME}.pid"
        printf "Starting iotagent ${NAME}..."
        status -p ${IOTAGENT_PID_FILE} ${EXECUTABLE} &> /dev/null 
        if [[ ${?} -eq 0 ]]; then
            printf "%s\n" " Already running, skipping $(success)"
            continue
        fi
        # Load the environment
        set -a
        source ${instance_config}
        # Mandatory parameters
        IOTAGENT_OPTS="   ${IS_MANAGER}              \
                       -n ${IOTAGENT_SERVER_NAME}    \
                       -v ${IOTAGENT_LOG_LEVEL}      \
                       -i ${IOTAGENT_SERVER_ADDRESS} \
                       -p ${IOTAGENT_SERVER_PORT}    \
                       -d ${IOTAGENT_LIBRARY_DIR}    \
                       -c ${IOTAGENT_CONFIG_FILE}"
        su ${USERNAME} -c "LD_LIBRARY_PATH=\"${IOTAGENT_LIBRARY_DIR}\" \
        ${EXECUTABLE} ${IOTAGENT_OPTS} & echo \$! > ${IOTAGENT_PID_FILE}" &> /dev/null 
        sleep 2 # wait some time to leave iotagent start
        local PID=$(cat ${IOTAGENT_PID_FILE})
        local var_pid=$(ps -ef | grep ${PID} | grep -v grep)
        if [[ -z "${var_pid}" ]]; then
            printf "%s" "pidfile not found"
            printf "%s\n" "$(failure)" 
            exit 1
        else
            printf "%s\n" "$(success)"
        fi
    done
    return ${result}
}
iotagent_stop()
{
    local result=0
    local iotagent_instance=${1}
    if [[ -z ${iotagent_instance} ]]; then
        list_run_instances="/var/run/iot/iotagent_*.pid"
    else
        list_run_instances="/var/run/iot/iotagent_${iotagent_instance}.pid"
    fi
    if [[ $(ls -l ${list_run_instances} 2> /dev/null | wc -l) -eq 0 ]]; then
        printf "%s\n" "There aren't any instance of IoTAgent ${iotagent_instance} running $(success)"
        return 0
    fi
    for run_instance in ${list_run_instances}
    do
        local NAME
        NAME=${run_instance%.pid}
        NAME=${NAME#*iotagent_}
        printf "%s" "Stopping IoTAgent ${NAME}..."
        local RUN_PID=$(cat ${run_instance})
        kill ${RUN_PID}  &> /dev/null
        local KILLED_PID=$(ps -ef | grep ${RUN_PID} | grep -v grep | awk '{print $2}')
        if [[ -z ${KILLED_PID} ]]; then
            printf "%s\n" "$(success)"
        else
            printf "%s\n" "$(failure)"
            result=$((${result}+1))
        fi
        rm -f ${run_instance} &> /dev/null 
    done
    return ${result}
}
iotagent_status()
{
    local result=0
    local iotagent_instance=${1}
    if [[ -z ${iotagent_instance} ]]; then
        list_run_instances="/var/run/iot/iotagent_*.pid"
    else
        list_run_instances="/var/run/iot/iotagent_${iotagent_instance}.pid"
    fi
    if [[ $(ls -l ${list_run_instances} 2> /dev/null | wc -l) -eq 0 ]]; then
        printf "%s\n" "There aren't any instance of IoTAgent ${iotagent_instance} running."
        return 1
    fi
    for run_instance in ${list_run_instances}
    do
        local NAME
        NAME=${run_instance%.pid}
        NAME=${NAME#*iotagent_}
        printf "%s\n" "IoTAgent ${NAME} status..."
        status -p ${run_instance} ${NODE_EXEC}
        result=$((${result}+${?}))
    done
    return ${result}
}
case ${PARAM} in
    'start')
        iotagent_start ${INSTANCE}
        ;;
    'stop')
        iotagent_stop ${INSTANCE}
        ;; 
    'restart')
        iotagent_stop ${INSTANCE}
        iotagent_start ${INSTANCE}
        ;;
    'status')
        iotagent_status ${INSTANCE}
        ;;
esac
Finally, you can find the logs file in /tmp/ :
IoTAgent-IoTPlatform.log    
IoTAgent.log    
IoTAgent-Manager.log
Hope it helps! :)