pin bundler to 2.2.11

It seems the latest 2.2.12 requires rake>13.0 installed and that
requirement doesn't work well in current our CI jobs.
Let's pin it to the previous version until we resolve the issue

Note that this change only covers library jobs and we also need the
same fix for puppet-openstack-integration later.

This change also removes the pin for the very old Ruby version.

Closes-Bug: #1917457
Change-Id: Ibafcb3b994db361df3427ca2afe4dd3d08028add

functions

@@ -27,9 +27,7 @@ install_gems() {
   # Install dependencies
   ruby <<EOF
 cmd = 'gem install bundler --no-document --verbose --bindir=${GEM_BIN_DIR}'
-if Gem::Version.new(RUBY_VERSION) < Gem::Version.new('2.3.0') then
-  cmd += ' -v 1.17.3'
-end
+cmd += ' -v 2.2.11'
 system(cmd)
 EOF
   $GEM_HOME/bin/bundle install