Docker: T7568: clean apt cache + clean some /tmp files

This saves ~50Mb for vyos-build image: 2.04Gb -> 1.99Gb
And ~19Mb for vyos image: 155Mb -> 136Mb

Docker stores all files created in each layer so
command

```
RUN wget -O /tmp/open-vmdk-master.zip https://github.com/.../master.zip && \
     unzip -d /tmp/ /tmp/open-vmdk-master.zip && \
     cd /tmp/open-vmdk-master/ && make && make install
```

will store open-vmdk-master.zip and /tmp/open-vmdk-master
in the image even though there is a cleanup command later:

```
RUN rm -rf /tmp/*
```

The cleanup command just makes these files invisible in last layer.

So temporary file must be removed in same RUN command
not to be stored in the image.

This commit adds such removals.

1 files changed, 5 insertions, 0 deletions

diff --git a/docker-vyos/Dockerfile b/docker-vyos/Dockerfile
index 0233817b..3fff371b 100644
--- a/docker-vyos/Dockerfile
+++ b/docker-vyos/Dockerfile
@@ -25,6 +25,8 @@ LABEL authors="VyOS Maintainers <maintainers@vyos.io>"
 ENV DEBIAN_FRONTEND noninteractive
 
 RUN /bin/echo -e 'APT::Install-Recommends "0";\nAPT::Install-Suggests "0";' > /etc/apt/apt.conf.d/01norecommends
+# Clean cache after each apt-get install command so that it is not stored in the image
+RUN /bin/echo -e 'DPkg::Post-Invoke {"/bin/rm -f /var/cache/apt/archives/*.deb /var/lib/apt/lists/* || true";};' > /etc/apt/apt.conf.d/clean
 
 # Base packaged needed to build packages and their package dependencies
 RUN apt-get update && apt-get install -y \
@@ -69,6 +71,9 @@ RUN bash /tmp/vyos_install_stage_03.sh
 # Delete installer scripts
 RUN rm -rf /tmp/*
 
+# Remove cleanup script so that in-container apt-get install uses cache
+RUN rm /etc/apt/apt.conf.d/clean
+
 
 # Make changes specific to the container environment