templates: handle empty docker tags properly

Even though 'latest' is the default tag name, there are some docker
images without tags. Tune the template to handle them properly
handle non-apt-based systems properly
properly set the metadata flag on the ruby variable
use a custom-made image for opensuse

The KIWI-based ones are weird when it comes to users (the
created user cannot even run /bin/ls ...).
filter out everything that has dev_mode=false and ruby!=1.9
disable debian testing

I just can't find a functional docker image for it.
add arch (untested)
updated autoproj_bootstrap-dev
bootstrap: add the 'dev' option to autoproj_bootstrap
RubyGems for ruby 2.0 on debian needs HOME to be set
use the -m option to useradd to create the home properly