[tests] test_corrupt_backup_content was updated [typos, new asserts]

[dmitry-lipetsk]

New names: full2_id [was fulle2_id] full1_conf_file [was fulle1_conf_file] full2_conf_file [was fulle2_conf_file]

New asserts:

• self.show_pb(backup_dir, 'node', full1_id)['status'] is 'CORRUPT'
• self.show_pb(backup_dir, 'node', full2_id)['status'] is 'OK'