[Dockerfiles] Used best practices for apt-get

See https://docs.docker.com/engine/userguide/eng-image/dockerfile_best-practices/#apt-get

- Replaced `-y install` with `install -y` (unification)

- Put every package on its own line

- Moved `rm -rf /var/lib/apt/lists/*` in the same `RUN` statement as `apt-get`

- Removed unnecessary `apt-get clean`
  See 03e2923e42/contrib/mkimage/debootstrap (L82-L105)

data/Dockerfiles/sogo/Dockerfile

@@ -5,8 +5,9 @@ ENV DEBIAN_FRONTEND noninteractive
 ENV LC_ALL C
 ENV GOSU_VERSION 1.9
 
-RUN apt-get update \
-	&& apt-get install -y --no-install-recommends apt-transport-https gnupg \
+RUN apt-get update && apt-get install -y --no-install-recommends \
+		apt-transport-https \
+		gnupg \
 		ca-certificates \
 		wget \
 		syslog-ng \
@@ -14,6 +15,7 @@ RUN apt-get update \
 		supervisor \
 		mysql-client \
 		cron \
+	&& rm -rf /var/lib/apt/lists/* \
 	&& dpkgArch="$(dpkg --print-architecture | awk -F- '{ print $NF }')" \
 	&& wget -O /usr/local/bin/gosu "https://github.com/tianon/gosu/releases/download/$GOSU_VERSION/gosu-$dpkgArch" \
 	&& wget -O /usr/local/bin/gosu.asc "https://github.com/tianon/gosu/releases/download/$GOSU_VERSION/gosu-$dpkgArch.asc" \
@@ -29,8 +31,10 @@ RUN touch /usr/share/doc/sogo/empty.sh
 
 RUN apt-key adv --keyserver keys.gnupg.net --recv-key 0x810273C4 \
 	&& echo "deb http://packages.inverse.ca/SOGo/nightly/3/debian/ jessie jessie" > /etc/apt/sources.list.d/sogo.list \
-	&& apt-get update \
-	&& apt-get -y --force-yes install sogo sogo-activesync 
+	&& apt-get update && apt-get install -y --force-yes \
+		sogo \
+		sogo-activesync \
+	&& rm -rf /var/lib/apt/lists/*
 
 RUN sed -i -E 's/^(\s*)system\(\);/\1unix-stream("\/dev\/log");/' /etc/syslog-ng/syslog-ng.conf
 RUN echo '* * * * *   sogo   /usr/sbin/sogo-ealarms-notify' > /etc/cron.d/sogo
@@ -42,4 +46,4 @@ COPY supervisord.conf /etc/supervisor/supervisord.conf
 
 CMD exec /usr/bin/supervisord -c /etc/supervisor/supervisord.conf
 
-RUN apt-get clean && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
+RUN rm -rf /tmp/* /var/tmp/*