List all known patches in repos.

def _get_patches(installed_only=False, root=None):
    '''
    List all known patches in repos.
    '''
    patches = {}
    for element in __zypper__(root=root).nolock.xml.call('se', '-t', 'patch').getElementsByTagName('solvable'):
        installed = element.getAttribute('status') == 'installed'
        if (installed_only and installed) or not installed_only:
            patches[element.getAttribute('name')] = {
                'installed': installed,
                'summary': element.getAttribute('summary'),
            }

    return patches