Make docker uid/gid explicit.

Closes #1034. Thanks to Daniele Sluijters.

docker/1.5/Dockerfile

@@ -67,8 +67,8 @@ RUN set -x && \
         WITH_WEBSOCKETS=yes \
         prefix=/usr \
         binary && \
-    addgroup -S mosquitto 2>/dev/null && \
+    addgroup -S -g 1883 mosquitto 2>/dev/null && \
-    adduser -S -D -H -h /var/empty -s /sbin/nologin -G mosquitto -g mosquitto mosquitto 2>/dev/null && \
+    adduser -S -u 1883 -D -H -h /var/empty -s /sbin/nologin -G mosquitto -g mosquitto mosquitto 2>/dev/null && \
     mkdir -p /mosquitto/config /mosquitto/data /mosquitto/log && \
     install -d /usr/sbin/ && \
     install -s -m755 /build/mosq/src/mosquitto /usr/sbin/mosquitto && \

docker/1.5/README.md

@@ -13,6 +13,11 @@ Two docker volumes have been created in the image to be used for persistent stor
 /mosquitto/log
 ```
 
+## User/Group
+
+The image runs mosqutto under the mosquitto user and group, which are created
+with a uid and gid of 1883.
+
 ## Configuration
 When creating a container from the image, the default configuration values are used.
 To use a custom configuration file, mount a **local** configuration file to `/mosquitto/config/mosquitto.conf`