Enhance zypper repo module: Changed the repo_exists function to respect .repo endings.

Changed the `repo_exists` function to respect `.repo` endings.
This is important, as a repo url is valid when ending on .repo instead of a slash.
The check of the existance of the .repo url in the output of
`zypper lr --uri`
would always fail, as `--uri` just shows the url variant with the trailing slash.