Correctly handle .repo files in zypper_repository module

Before the changes, removing a repository required a repo url. This shouldn't be required since zypper allows removing a repo based on its alias (mapped to name in this module).

The name variable was always required, which is misleading since repofiles provide their own alias. So a runtime check was added to avoid this confusion.

Additionaly, running this module on .repo files weren't idempotent. e.g

Before:
$ ./hacking/test-module -m library/packaging/zypper_repository -a "repo=http://download.opensuse.org/repositories/devel:/languages:/python/SLE_11_SP3/devel:languages:python.repo name=foo"
{"repo": "http://download.opensuse.org/repositories/devel:/languages:/python/SLE_11_SP3/devel:languages:python.repo", "state": "present", "changed": true}
$ ./hacking/test-module -m library/packaging/zypper_repository -a "repo=http://download.opensuse.org/repositories/devel:/languages:/python/SLE_11_SP3/devel:languages:python.repo name=foo"
{"msg": "Repository named 'devel_languages_python' already exists. Please use another alias.\n", "failed": true}

After:
$ ./hacking/test-module -m library/packaging/zypper_repository -a "repo=http://download.opensuse.org/repositories/devel:/languages:/python/SLE_11_SP3/devel:languages:python.repo"
{"repo": "http://download.opensuse.org/repositories/devel:/languages:/python/SLE_11_SP3/devel:languages:python.repo", "state": "present", "changed": true}
$ ./hacking/test-module -m library/packaging/zypper_repository -a "repo=http://download.opensuse.org/repositories/devel:/languages:/python/SLE_11_SP3/devel:languages:python.repo"
{"repo": "http://download.opensuse.org/repositories/devel:/languages:/python/SLE_11_SP3/devel:languages:python.repo", "state": "present", "changed": false}

Signed-off-by: Hector Acosta <hector.acosta@gmail.com>