containers/ws: improve caching for incremental builds

When iterating locally it helps if we can avoid having to repeat the
"download the packages from the Fedora servers" step, which is currently
run every time.

We can do that by separating it to a separate step that runs *before* we
copy in the entire contents of what becomes the /container directory
(which changes on every iteration).

We install cockpit-bridge and cockpit-ws up front now even though they
will still be installed later by install.sh because we want the
dependencies (and I couldn't find any easy way to say "just install the
runtime dependencies of these packages).

We don't bother with any "layer avoidance" techniques here because this
is just the builder container which doesn't become part of the final
result.

Author: allisonkarlitskaya

containers/ws/Containerfile

@@ -3,8 +3,26 @@ LABEL maintainer="cockpit-devel@lists.fedorahosted.org"
 LABEL VERSION=main
 
 ARG VERSION
-ADD . /container
 
+# This goes into the builder container
+RUN dnf install -y 'dnf-command(download)' cpio
+
+# This goes into the final container.  The cockpit- packages can be replaced
+# with local builds by the install.sh script later.
+RUN dnf install -y \
+		--installroot=/build \
+		--setopt=install_weak_deps=False \
+		--use-host-config \
+	cockpit-bridge \
+	cockpit-ws \
+	coreutils-single \
+	openssh-clients \
+	sed \
+	sscg \
+	util-linux-core \
+	;
+
+ADD . /container
 RUN /container/install.sh
 
 FROM scratch

containers/ws/install.sh

@@ -4,7 +4,7 @@ set -ex
 
 OSVER=$(. /etc/os-release && echo "$VERSION_ID")
 INSTALLROOT=/build
-INSTALL="dnf install -y --installroot=$INSTALLROOT --releasever=$OSVER --setopt=install_weak_deps=False --use-host-config"
+INSTALL="dnf install -y --installroot=$INSTALLROOT --setopt=install_weak_deps=False --use-host-config"
 
 # keep in sync with test/ws-container.install
 PACKAGES="
@@ -21,9 +21,6 @@ EXTERNAL_COCKPIT_PACKAGES="
 cockpit-files
 "
 
-dnf install -y 'dnf-command(download)' cpio
-$INSTALL coreutils-single util-linux-core sed sscg python3 openssh-clients
-
 arch=`uname -p`
 rpm=$(ls /container/rpms/cockpit-ws-*$OSVER.*$arch.rpm /container/rpms/cockpit-bridge-*$OSVER.*$arch.rpm || true)