[dist] Install thor v0.19 directly as a gem

foreman, which we only run in docker, needs a different thor version than OBS.
Installing the gem directly spares us from having to rpm package two different thor versions.

Packages libffi48-devel and autoconf are needed to install ffi gem.

Dockerfile

@@ -17,6 +17,9 @@ RUN chown -R frontend /obs/src/api
 # builds this container
 USER frontend
 WORKDIR /obs/src/api
+# foreman, which we only run in docker, needs a different thor version than OBS.
+# Installing the gem directly spares us from having to rpm package two different thor versions.
+RUN gem install thor:0.19 foreman
 
 # FIXME: Retrying bundler if it fails is a workaround for https://github.com/moby/moby/issues/783
 #        which seems to happen on openSUSE (< Tumbleweed 20171001)...

contrib/docker-bootstrap.sh

@@ -12,8 +12,9 @@ do
       git-core \
       ruby2.4-devel cyrus-sasl-devel openldap2-devel libxml2-devel zlib-devel libxslt-devel \
       perl-XML-Parser \
+      libffi48-devel autoconf \
       ruby2.4-rubygem-mysql2 \
-      ruby2.4-rubygem-bundler ruby2.4-rubygem-thor ruby2.4-rubygem-foreman
+      ruby2.4-rubygem-bundler
     ;;
 
   backend)