Workaround Kiwi issue by escaping repository aliases

Kiwi has an issue if the repository alias has spaces which results
in the image building to fail so we are replacing spaces by dashes.
This should have no influence on the final image since zypper adds
the repository with the old name.
Merge pull request #381 from SUSE/workaround_kiwi_alias_issue

Workaround Kiwi issue by escaping repository aliases