Allow Autoyast export only if packages and repositories are present
Adapt Autoyast export readme to current implementation

It is much easier to user Autoyast2 since the network is setup
automatically.

It is also not needed to provide the URL manually anymore
after Autoyast is started.
Use Dir[..] with sort to prevent different results

It seems that older Ruby versions (before openSUSE 13.2) have a different
order of the file list than newer ones. This shouldn't happen with sort.
Merge pull request #440 from SUSE/some_autoyast_fixes

Some autoyast fixes