Allow customer jars for plugins

[hae-anwar-bardai]

Hi All,
There is a need for the build pack to support local jars for plug-ins. Will appreciate adding it in your repo.

        PLUGIN_JAR="${PLUGIN_NAME}-${PLUGIN_VERSION}.jar"
        PLUGIN_PATH="${BUILD_DIR}/sonarqube/extensions/plugins/${PLUGIN_JAR}"

        if [[ -f ${BUILD_DIR}/${PLUGIN_JAR} ]];
        then
            cp ${BUILD_DIR}/${PLUGIN_JAR} ${PLUGIN_PATH}
        else
            PLUGIN_URL="${SONARQUBE_DIST_URL}/${PLUGIN_NAME}/${PLUGIN_JAR}"
            wget ${PLUGIN_URL} -O "${PLUGIN_PATH}" --no-check-certificate -q
        fi

Thanks