[Buildroot] [git commit] support/docker: run apt-get update and apt-get install in two RUNs

[Thomas Petazzoni]

commit: https://git.buildroot.net/buildroot/commit/?id=c4f844ff3212266f845ea812da2a8647a9f1e136
branch: https://git.buildroot.net/buildroot/commit/?id=refs/heads/master

In commit 7517aef4d (support/docker: limit the number of layers),
we reduced the number of layers by coalescing multiple RUN commands
into less commands.

In doing so, we especially coalesced "apt-get update" with "apt-get
install".

However, the distribution we used is a pinned version of stretch, so
we know that running apt-get update will always yield the same apt
database.

If we split the two apt-get commands, then we can re-use any local
intermediate image when we need to update the list of packages to
install; this helps quite a bit when testing the docker files over
and over again, with just slight variants in the packages list.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998 at free.fr>
Cc: Ricardo Martincoski <ricardo.martincoski at gmail.com>
Cc: Peter Korsgaard <peter at korsgaard.com>
Reviewed-by: Ricardo Martincoski <ricardo.martincoski at gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni at bootlin.com>
---
 support/docker/Dockerfile | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/support/docker/Dockerfile b/support/docker/Dockerfile
index f01ac25f93..8c525f7cf1 100644
--- a/support/docker/Dockerfile
+++ b/support/docker/Dockerfile
@@ -20,8 +20,8 @@ COPY apt-sources.list /etc/apt/sources.list
 
 # The container has no package lists, so need to update first
 RUN dpkg --add-architecture i386 && \
-    apt-get update -y && \
-    apt-get install -y --no-install-recommends \
+    apt-get update -y
+RUN apt-get install -y --no-install-recommends \
         build-essential cmake libc6:i386 g++-multilib \
         bc ca-certificates file locales rsync \
         cvs bzr git mercurial subversion wget \