Expand update block for readability and add cleanup

docker/amd64/Dockerfile

@@ -1,6 +1,19 @@
 FROM amd64/ubuntu:18.04
 
-RUN apt-get update -qq && apt-get install -y wget unzip cmake make build-essential git python3 python3-pip
+ARG DEBIAN_FRONTEND=noninteractive
+RUN apt-get update -qq \
+    && apt-get install -y \ 
+        build-essential \
+        cmake \
+        git \
+        make \
+        python3 \
+        python3-pip \
+        tar \
+        unzip \
+        wget \
+    && rm -rf /var/cache/apt/* /var/lib/apt/lists/*
+
 RUN wget -q https://developer.arm.com/-/media/Files/downloads/gnu-rm/9-2020q2/gcc-arm-none-eabi-9-2020-q2-update-x86_64-linux.tar.bz -O - | tar -xj -C /opt/
 RUN wget -q https://developer.nordicsemi.com/nRF5_SDK/nRF5_SDK_v15.x.x/nRF5_SDK_15.3.0_59ac345.zip && unzip -q nRF5_SDK_15.3.0_59ac345.zip -d /opt/ && rm nRF5_SDK_15.3.0_59ac345.zip
 

docker/arm64v8/Dockerfile

@@ -1,6 +1,22 @@
 FROM arm64v8/ubuntu:18.04
 
-RUN apt-get update -qq && apt-get install -y wget unzip cmake make build-essential git python3 python3-pip libffi-dev libssl-dev python3-dev
+ENV DEBIAN_FRONTEND=noninteractive
+RUN apt-get update -qq \
+    && apt-get install -y \ 
+        build-essential \
+        cmake \
+        git \
+        libffi-dev \
+        libssl-dev \
+        make \
+        python3 \
+        python3-dev \
+        python3-pip \
+        tar \
+        unzip \
+        wget \
+    && rm -rf /var/cache/apt/* /var/lib/apt/lists/*
+
 RUN wget -q https://developer.arm.com/-/media/Files/downloads/gnu-rm/9-2020q2/gcc-arm-none-eabi-9-2020-q2-update-aarch64-linux.tar.bz2 -O - | tar -xj -C /opt/
 RUN wget -q https://developer.nordicsemi.com/nRF5_SDK/nRF5_SDK_v15.x.x/nRF5_SDK_15.3.0_59ac345.zip && unzip -q nRF5_SDK_15.3.0_59ac345.zip -d /opt/ && rm nRF5_SDK_15.3.0_59ac345.zip