Update alpine linux base to 3.7, and dependencies

Runtime libraries
- librdkafka (0.9.5-r0 -> 0.11.1-r1)
  * Use of rd_kafka_last_error() instead of global errno
  * Defaulting `queue.buffering.max.ms` to 1000ms
  * Applying topics properties to kafka handler

- musl (1.1.16-r14 -> 1.1.18-r2)

Devel tools
- libatomic (6.3.0-r4 -> 6.4.0-r5)
- gcc (6.3.0-r4 -> 6.4.0-r5)
- fortify-headers (0.8-r0 -> 0.9-r0)
- expat (2.2.0-r1 -> 2.2.5-r0)
- gdb (7.12.1-r1 -> 8.0.1-r3)
- cgdb (0.7.0-r0 -> 0.7.0-r1)
- expat-dev (2.2.0-r1 -> 2.2.5-r0)
- guile (2.0.13-r0 -> 2.0.14-r0)
- libbz2 (1.0.6-r5 -> 1.0.6-r6)
- libarchive-tools (3.3.1-r2 -> 3.3.2-r2)
- net-snmp-libs (5.7.3-r8 -> 5.7.3-r10)
- python3 (3.6.1-r3 -> 3.6.3-r9)
- valgrind (3.12.0-r1)

docker/Dockerfile.m4

@@ -1,15 +1,12 @@
-FROM alpine:3.6
+FROM alpine:3.7
 
 # envsubst (gettext is very big! install only binary & dependency)
 RUN apk add --no-cache libintl gettext && \
         cp /usr/bin/envsubst /usr/local/bin/envsubst && \
         apk del gettext
 
 # Common C runtime libraries
-RUN apk add --no-cache librdkafka jansson zlib
-
-# n2k libraries
-RUN apk add --no-cache yajl libmicrohttpd libev
+RUN apk add --no-cache librdkafka zlib
 
 # ca-certificates: for wget bootstrapping
 # ncurses - expat: deps for xml-coreutils

src/main.c

@@ -553,8 +553,7 @@ static int worker_process_sensor_send_array(struct _worker_info *worker_info,
 				rdlog(LOG_ERR,
 				      "[Kafka] Cannot produce kafka message: "
 				      "%s",
-				      rd_kafka_err2str(rd_kafka_errno2err(
-						      errno)));
+				      rd_kafka_err2str(rd_kafka_last_error()));
 			}
 		} /* if kafka */
 
@@ -762,6 +761,9 @@ int main(int argc, char *argv[]) {
 	worker_info.rk_conf = rd_kafka_conf_new();
 	worker_info.rkt_conf = rd_kafka_topic_conf_new();
 
+	// Default to librdkafka pre-0.11 behavior:
+	rd_kafka_conf_set(worker_info.rk_conf, "linger.ms", "1000", NULL, 0);
+
 	pthread_t *pd_thread = NULL;
 	rd_fifoq_t queue;
 	sensor_queue_init(&queue);