automation: try to keep openSUSE Leap image a little smaller

Using `--no-recommends` when updating or installing commands should
prevent non strictly necessary packages to be installed.

doing a `clean -a` after installing all the packages, should, in
theory, free more space (as opposed to using just `clean`).

Signed-off-by: Dario Faggioli <dfaggioli@suse.com>
Acked-by: Doug Goldstein <cardoe@cardoe.com>

automation/build/suse/opensuse-leap.dockerfile

@@ -7,8 +7,8 @@ ENV USER root
 RUN mkdir /build
 WORKDIR /build
 
-RUN zypper ref && zypper up -y
-RUN zypper install -y \
+RUN zypper ref && zypper up -y --no-recommends
+RUN zypper install -y --no-recommends \
         acpica \
         bc \
         bin86 \
@@ -65,4 +65,4 @@ RUN zypper install -y \
         xz-devel \
         zlib-devel \
         && \
-        zypper clean
+        zypper clean -a