Build: Only Bundle Gems on SLES 11

This gives minimal runtime dependencies on SLES 11, which happens
to be an environment where Bundler can actually be used to bundle
already-installed Gems into the RPM at build time.  This doesn't
work on other distros (e.g. Fedora) and has changing requirements
on different versions of openSUSE (e.g.: some versions will fail
to bundle rake as it's actually provided by ruby), so for all other
distros and versions we just have a runtime dependency on Rails
etc. rather than using Bundler.

Signed-off-by: Tim Serong <tserong@suse.com>
Misc: Don't require rails-i18n

AIUI rails-i18n shouldn't be necessary as we're not using ActiveRecord
anyway.

Signed-off-by: Tim Serong <tserong@suse.com>