Improve extraction of available updates

[smortex]

Pull Request (PR) description

The yum list updates command outputs diagnostic messages and then the actual available updates both on stdout. Depending on the installed yum plugins, a variable number of diagnostic lines are emitted, and the output is always formatted for humans, making it non-trivial to distinguish useless and relevant lines.

Instead of ignoring the first line, match each line with a pattern matching the following fields:

• package: The name of the package for which an update is available, they are in the format <package-name>.<architecture>;
• available_version: The version of the package available for update, ensure it starts with a digit;
• repository: The repository containing the update

These fields are separated by a variable amount of space. When a line match this pattern, consider the package as relevant for update.

This Pull Request (PR) fixes the following issues

Fixes #180

[smortex]

@vchepkov, can you please confirm that this fix your problem?

[bastelfreak]

thanks for the PR. can you add an acceptance test that verifies your changes are correct? The regex is quite hard to read :)

[smortex]

I could finally managed to get some time for this. I added a few unit test and rebased the fix on top of master. Thanks!